Fig. 41.—Cuvier as a Young Man, 1769-1832.
His Physiognomy.—It is very interesting to note in his portraits the change in his physiognomy accompanying his transformation from a young man of provincial appearance into an elegant personage. Fig. 41 shows his portrait in the early days when he was less mindful of his personal appearance. It is the face of an eager, strong, young man, still retaining traces of his provincial life. His long, light-colored hair is unkempt, but does not hide the magnificent proportions of his head. Fig. 42 shows the growing refinement of features which came with his advancement, and the aristocratic look of supremacy which set upon his countenance afterhis wide recognition passing by a gradation of steps from the position of head of the educational system, to that of baron and peer of France.
Fig. 42.—Cuvier at the Zenith of His Power.
Cuvier was a man of commanding power and colossal attainments; he was a favorite of Napoleon Bonaparte, who elevated him to office and made him director of the higher educational institutions of the Empire. But to whatever place of prominence he attained in the government, he neverlost his love for natural science. With him this was an absorbing passion, and it may be said that he ranks higher as a zoölogist than as a legislator.
Comprehensiveness of Mind.—Soon after his arrival in Paris he began to lecture upon comparative anatomy and to continue work in a most comprehensive way upon the subjects which he had cultivated at Caen. He saw everything on a large scale. This led to his making extensive studies of whatever problems engaged his mind, and his studies were combined in such a manner as to give a broad view of the subject.
Indeed, comprehensiveness of mind seems to have been the characteristic which most impressed those who were acquainted with him. Flourens says of him: "Ce qui caractérise partout M. Cuvier, c'est l'esprit vaste." His broad and comprehensive mind enabled him to map out on great lines the subject of comparative anatomy. His breadth was at times his undoing, for it must be confessed that when the details of the subject are considered, he was often inaccurate. This was possibly owing to the conditions under which he worked; having his mind diverted into many other channels, never neglecting his state duties, it is reasonable to suppose that he lacked the necessary time to prove his observations in anatomy, and we may in this way account for some of his inaccuracies.
Besides being at fault in some of his comparative anatomy, he adhered to a number of ideas that served to retard the progress of science. He was opposed to the ideas of his contemporary Lamarck, on the evolution of animals. He is remembered as the author of the dogma of catastrophism in geology. He adhered to the old notion of the pre-formation of the embryo, and also to the theory of the spontaneous origin of life.
Founds Comparative Anatomy.—Regardless of this qualification, he was a great and distinguished student, andfounded comparative anatomy. From 1801 to 1805 appeared hisLeçons d' Anatomie Comparée, a systematic treatise on the comparative anatomy of animals, embracing both the invertebrates and the vertebrates. In 1812 was published his great work on the fossil bones about Paris, an achievement which founded the science of vertebrate palæontology. His extensive examination of the structure of fishes also added to his already great reputation. His book on the animal kingdom (Le Règne Animal distribué d'après son Organisation, 1816), in which he expounded his type-theory, has been considered in a previous chapter.
He was also deeply interested in the historical development of science, and his volumes on the rise of the natural sciences give us almost the best historical estimate of the progress of science that we have at the present day.
His Domestic Life.—Mrs. Lee, in a chatty account of Cuvier, shows one of his methods of work. He had the faculty of making others assist him in various ways. Not only members of his family, but also guests in his household were pressed into service. They were invited to examine different editions of works and to indicate the differences in the plates and in the text. This practice resulted in saving much time for Cuvier, since in the preparation of his historical lectures he undertook to examine all the original sources of the history with which he was engaged. In his lectures he summarized facts relating to different editions of books, etc.
Mrs. Lee also gives a picture of his family life, which was, to all accounts, very beautiful. He was devoted to his wife and children, and in the midst of exacting cares he found time to bind his family in love and devotion. Cuvier was called upon to suffer poignant grief in the loss of his children, and his direct family was not continued. He was especially broken by the death of his daughter who had grown to young womanhood and was about to be married.
From the standpoint of a sincere admirer, Mrs. Lee writes of his generosity and nobility of temperament, declaring that his career demonstrated that his mind was great and free from both envy and smallness.
Some Shortcomings.—Nevertheless, there are certain things in the life of Cuvier that we wish might not have been. His break with his old friends Lamarck and Saint-Hilaire seems to show a domination of qualities that were not generous and kindly; those observations of Lamarck showing a much profounder insight than any of which he himself was the author were laughed to scorn. His famous controversy with Saint-Hilaire marks a historical moment that will be dealt with in the chapter on Evolution.
George Bancroft, the American historian, met him during a visit to Paris in 1827. He speaks of his magnificent eyes and his fine appearance, but on the whole Cuvier seems to have impressed Bancroft as a disagreeable man.
Some of his shortcomings that served to retard the progress of science have been mentioned. Still, with all his faults, he dominated zoölogical science at the beginning of the nineteenth century, and so powerful was his influence and so undisputed was his authority among the French people that the rising young men in natural science sided with Cuvier even when he was wrong. It is a noteworthy fact that France, under the influence of the traditions of Cuvier, was the last country slowly and reluctantly to harbor as true the ideas regarding the evolution of animal life.
Cuvier's Successors
While Cuvier's theoretical conclusions exercised a retarding influence upon the progress of biology, his practical studies more than compensated for this. It has been pointed out how his type-theory led to the reform of the Linnæansystem, but, besides this, the stimulus which his investigations gave to studies in comparative anatomy was even of more beneficent influence. As time passed the importance of comparative anatomy as one division of biological science impressed itself more and more upon naturalists. A large number of investigators in France, England, and Germany entered the field and took up the work where Cuvier had left it. The more notable of these successors of Cuvier should come under consideration.
Fig. 43.—H. Milne-Edwards, 1800-1885.
His intellectual heirs in France were Milne-Edwards and Lacaze-Duthiers.
Milne-Edwards.—H. Milne-Edwards (1800-1885) was a man of great industry and fine attainments; prominent alike in comparative anatomy, comparative physiology, and general zoölogy, professor for many years at the Sorbonne in Paris.In 1827 he introduced into biology the fruitful idea of the division of physiological labor. He completed and published excellent researches upon the structure and development of many animals, notably crustacea, corals, etc. His work on comparative anatomy took the form of explanations of the activities of animals, or comparative physiology. His comprehensive treatiseLeçons sur la Physiologie et l'Anatomie Comparée, in fourteen volumes, 1857-1881, is a mine of information regarding comparative anatomy as well as the physiology of organisms.
Fig. 44.—Lacaze-Duthiers, 1821-1901.
Lacaze-Duthiers.—Henri de Lacaze-Duthiers (1821-1901), the man of comprehensive mind, stimulating as an instructor of young men, inspiring other workers, and producing a large amount of original research on his own account, director of the Seaside Stations at Roscoff and Banyuls, the founder of a noteworthy periodical of experimental zoölogy—this great man, whose portrait is shown in Fig. 44, was one of the leading comparative anatomists in France.
Fig. 45.—Lorenzo Oken, 1779-1851.
R. Owen.—In England Richard Owen (1804-1892) carried on the influence of Cuvier. At the age of twenty-seven he went to Paris and renewed acquaintance with the great Cuvier, whom he had met the previous year in England. He spent some time at the Jardin des Plantes examining the extensive collections in the museum. Although the idea was repudiated by Owen and some of his friends, it is not unlikely that the collections of fossil animals and the researches upon them which engaged Cuvier at that time had great influence upon the subsequent studies of Owen. Although he never studied under Cuvier, in a sense he may be regarded as his disciple. Owen introduced into anatomy the important conceptions of analogy and homology, the former being a likeness based upon the use to which organs are put, as the wing of a butterfly and the wing of a bat; while homology is a true relationship founded on likeness in structure and development, asthe wing of a bat and the foreleg of a dog. Analogy is a superficial, and often a deceiving relationship; homology is a true genetic relationship. It is obvious that this distinction is of great importance in comparing the different parts of animals. He made a large number of independent discoveries, and published a monumental work on the comparativeanatomy of vertebrates (1866-68). In much of his thought he was singular, and many of his general conclusions have not stood the test of time. He undertook to establish the idea of an archtype in vertebrate anatomy. He clung to the vertebral theory of the skull long after Huxley had shown such a theory to be untenable. The idea that the skull is made up of modified vertebrae was propounded by Goethe and Oken. In the hands of Oken it became one of the anatomical conclusions of the school ofNaturphilosophie. This school of transcendental philosophy was founded by Schelling, and Oken (Fig. 45) was one of its typical representatives. The vertebral theory of the skull was, therefore, not original with Owen, but he adopted it, greatly elaborated it, andclung to it blindly long after the foundations upon which it rested were removed.
Fig. 46.—Richard Owen, 1804-1892.
Richard Owen (Fig. 46) was succeeded by Huxley (1825-1895), whose exactness of observation and rare judgment as to the main facts of comparative anatomy mark him as one of the leaders in this field of research. The influence of Huxley as a popular exponent of science is dealt with in a later chapter.
Meckel.—Just as Cuvier stands at the beginning of the school of comparative anatomy in France, so does J. Fr. Meckel in Germany. Meckel (1781-1833) was a man of rare talent, descended from a family of distinguished anatomists. From 1804 to 1806 he studied in Paris under Cuvier, and when he came to leave the French capital to become professor of anatomy at Halle, he carried into Germany the teachings and methods of his master. He was a strong force in the university, attracting students to his department by his excellent lectures and his ability to arouse enthusiasm. Some of these students were stimulated to undertake researches in anatomy, and there came from his laboratory a number of investigations that were published in a periodical which he founded. Meckel himself produced many scientific papers and works on comparative anatomy, which assistedmaterially in the advancement of that science. His portrait, which is rare, is shown in Fig. 47.
Fig. 47.—J. Fr. Meckel, 1781-1833.
Rathke.—Martin Henry Rathke (1793-1860) greatly advanced the science of comparative anatomy by insisting upon the importance of elucidating anatomy with researches in development. This is such an important consideration that his influence upon the progress of comparative anatomy can not be overlooked. After being a professor in Dorpat, he came, in 1835, to occupy the position of professor of anatomy and zoölogy at Königsberg, which had been vacated by Von Baer on the removal of the latter to St. Petersburg. His writings are composed with great intelligence, and his facts are carefully coördinated. Rathke belonged to the good old school of German writers whose researches were profound and extensive, and whose expression was clear, being based upon matured thought. His papers on the aortic arches and the Wolffian body are those most commonly referred to at the present time.
Müller.—Johannes Müller (1801-1858), that phenomenal man, besides securing recognition as the greatest physiologist of the nineteenth century, also gave attention to comparative anatomy, and earned the title of the greatest morphologist of his time. His researches were so accurate, so complete, so discerning, that his influence upon the development of comparative anatomy was profound. Although he is accorded, in history, the double distinction of being a great anatomist and a great physiologist, his teaching tended to physiology; and most of his distinguished students were physiologists of the broadest type, uniting comparative anatomy with their researches upon functional activities. (For Müller's portrait see p. 187.)
Gegenbaur.—In Karl Gegenbaur (1826-1903) scientific anatomy reached its highest expression. His work was characterized by broad and masterly analysis of the facts of structure, to which were added the ideas derived from the study of the development of organs. He was endowed with an intensely keen insight, an insight which enabled him to separate from the vast mass of facts the important and essential features, so that they yielded results of great interest and of lasting importance. This gifted anatomist attracted many young men from the United States and from other countries to pursue under his direction the study of comparative anatomy. He died in Heidelberg in 1903, where he had been for many years professor of anatomy in the university.
Fig. 48.—Karl Gegenbaur, 1826-1903.
In the group of living German anatomists the names of Fürbringer, Waldeyer, and Wiedersheim can not go unmentioned.
E.D. Cope.—In America the greatest comparative anatomist was E.D. Cope (1840-1897), a man of the highest order of attainment, who dealt with the comparative anatomy not only of living forms, but of fossil life, and made contributions of a permanent character to this great science; a man whose title to distinction in the field of comparative anatomy will become clearer to later students with the passage of time. For Cope's portrait see p. 336.
Of the successors of Cuvier, we would designate Meckel, Owen, Gegenbaur, and Cope as the greatest.
Comparative anatomy is a very rich subject, and when elucidated by embryology, is one of the firm foundations of biology. If we regard anatomy as a science of statics, we recognize that it should be united with physiology, which represents the dynamical side of life. Comparative anatomy and comparative physiology should go hand in hand in the attempt to interpret living forms. Advances in these two subjects embrace nearly all our knowledge of living organisms. It is a cause for congratulation that comparative anatomy has now become experimental, and that gratifying progress is being made along the line of research designated as experimental morphology. Already valuable results have been attained in this field, and the outlook of experimental morphology is most promising.
CHAPTER VIII
BICHAT AND THE BIRTH OF HISTOLOGY
Wemust recognize Bichat as one of the foremost men in biological history, although his name is not well known to the general public, nor constantly referred to by biologists as that of one of the chief luminaries of their science. In him was combined extraordinary talent with powers of intense and prolonged application; a combination which has always produced notable results in the world. He died at the age of thirty-one, but, within a productive period of not more than seven years, he made observations and published work that created an epoch and made a lasting impression on biological history.
His researches supplemented those of Cuvier, and carried the analysis of animal organization to a deeper level. Cuvier laid the foundations of comparative anatomy by dissecting and arranging in a comprehensive system the organs of animals, but Bichat went a step further and made a profound study of the tissues that unite to make up the organs. As we have already noted in a previous chapter, this was a step in reaching the conception of the real organization of living beings.
Buckle's Estimate of Bichat.—It is interesting to note the impression made by Bichat upon one of the greatest students of the history of civilization. Buckle says of him: "Great, however, as is the name of Cuvier, a greater still remains behind. I allude, of course, to Bichat, whose reputation is steadily advancing as our knowledge advances; who, if we compare the shortness of his life with the reach and depth of his views, must be pronounced the most profound thinker and consummate observer by whom the organization of the animal frame has yet been studied.
"We may except Aristotle, but between Aristotle and Bichat I find no middle man."
Whether or not we agree fully with this panegyric of Buckle, we must, I think, place Bichat among the most illustrious men of biological history, as Vesalius, J. Müller, Von Baer, and Balfour.
Marie François Xavier Bichat was born in 1771 at Thoirette, department of the Ain. His father, who was a physician, directed the early education of his son and had the satisfaction of seeing him take kindly to intellectual pursuits. The young student was distinguished in Latin and mathematics, and showed early a fondness for natural history. Having elected to follow the calling of his father, he went to Lyons to study medicine, and came under the instruction of Petit in surgery.
Bichat in Paris.—It was, on the whole, a fortunate circumstance for Bichat that the turbulent events of the French Revolution drove him from Lyons to Paris, where he could have the best training, the greatest stimulus for his growth, and at the same time the widest field for the exercise of his talents. We find him in Paris in 1793, studying under the great surgeon Desault.
He attracted attention to himself in the class of this distinguished teacher and operator by an extemporaneous report on one of the lectures. It was the custom in Desault's classes to have the lectures of the professor reported upon before an assistant by some student especially appointed for the purpose. On one occasion the student who had been appointed to prepare and deliver the review was absent, and Bichat,who was gifted with a powerful memory, volunteered without previous notice to take his place. The lecture was a long and difficult one on the fractures of the clavicle, but Bichat's abstract was so clear, forceful, and complete that its delivery in well-chosen language produced a great sensation both upon the instructor and the students. This notable performance served to bring him directly to the attention of Desault, who invited him to become his assistant and to live in his family. The association of Bichat with the great surgeon was most happy. Desault treated him as a son, and when he suddenly died in 1795, the care of preparing his works for the printer was left to Bichat.
The fidelity with which Bichat executed this trust was characteristic of his noble nature. He laid aside his own personal interests, and his researches in which he was already immersed, and by almost superhuman labor completed the fourth volume of Desault'sJournal of Surgeryand at the same time collected and published his scattered papers. To these he added observations of his own, making alterations to bring the work up to the highest plane. Thus he paid the debt of gratitude which he felt he owed to Desault for his friendship and assistance.
In 1797 he was appointed professor of anatomy, at the age of twenty-six, and from then to the end of his life, in 1801, he continued in his career of remarkable industry.
The portrait of this very attractive man is shown in Fig. 49. His face shows strong intellectuality. He is described as of "middling stature, with an agreeable face lighted by piercing and expressive eyes." He was much beloved by his students and associates, being "in all relations of life most amiable, a stranger to envy or other hateful passions, modest in demeanor and lively in his manners, which were open and free."
His Phenomenal Industry.—His industry was phenomenal; besides doing the work of a professor, he attended to a considerable practice, and during a single winter he is said to have examined with care six hundred bodies in the pursuance of his researches upon pathological anatomy.
Fig. 49.—Bichat, 1771-1801.
In the year 1800, when he was thirty years old, began to appear the results of his matured researches. We speak of these as being matured, not on account of his age or the great number of years he had labored upon them, but from theintensity and completeness with which he had pursued his investigations, thus giving to his work a lasting quality.
First came his treatise on the membranes (Traité des Membranes); followed quickly by his Physiological Researches into the Phenomena of Life and Death (Recherches Physiologiques sur la Vie et la Mort); then appeared his General Anatomy (Anatomie Générale) in 1801, and his treatise upon Descriptive Anatomy, upon which he was working at the time of his death.
His death occurred in 1801, and was due partly to an accident. He slipped upon the stairs of the dissecting-room, and his fall was followed by gastric derangement, from which he died.
Results of His Work.—The new science of the anatomy of the tissues which he founded is now known as histology, and the general anatomy, as he called it, has now become the study of minute anatomy of the tissues. Bichat studied the membranes or tissues very profoundly, but he did not employ the microscope and make sketches of their cellular construction. The result of his work was to set the world studying the minute structure of the tissues, a consequence of which led to the modern study of histology. Since this science was constructed directly upon his foundation, it is proper to recognize him as the founder of histology.
Carpenter says of him: "Altogether Bichat left an impress upon the science of life, the depth of which can scarcely be overrated; and this not so much by the facts which he collected and generalized, as by the method of inquiry which he developed, and by the systematic form which he gave to the study of general anatomy in its relations both to physiology and pathology."
Bichat's More Notable Successors.—His influence extended far, and after the establishment of the cell-theory took on a new phase. Microscopic study of the tissues hasnow become a separate division of the science of anatomy, and engages the attention of a very large number of workers. While the men who built upon Bichat's foundation are numerous, we shall select for especial mention only a few of the more notable, as Schwann, Koelliker, Schultze, Virchow, Leydig, and Ramon y Cajal, whose researches stand in the direct line of development of the ideas promulgated by Bichat.
Schwann.—Schwann's cell-theory was the result of close attention to the microscopic structure of the tissues of animals. It was an extension of the knowledge of the tissues which Bichat distinguished and so thoroughly investigated from other points of view. The cell-theory, which took rise in 1839, was itself epoch-making, and the science of general anatomy was influenced by it as deeply as was the science of embryology. The leading founder of this theory was Theodor Schwann, whose portrait is shown on page 245, where there is also a more extended account of his labors in connection with the cell-theory. Had not the life of Bichat been cut off in his early manhood, he might well have lived to see this great discovery added to his own.
Koelliker.—Albrecht von Koelliker (1817-1905) was one of the greatest histologists of the nineteenth century. He is a striking figure in the development of biology in a general way, distinguished as an embryologist, as a histologist, and in other connections. During his long life, from 1817 to 1905, he made an astounding number of additions to our knowledge of microscopic anatomy. In the early years of his scientific activity, "he helped in establishing the cell-theory, he traced the origin of tissues from the segmenting ovum through the developing embryo, he demonstrated the continuity between nerve-fibers and nerve-cells of vertebrates (1845), ... and much more." He is mentioned further, in connection with the rise of embryology, in Chapter X.
The strong features of this veteran of research are shown in the portrait, Fig. 50, which represents him at the age of seventy.
In 1847 he was called to the University of Würzburg, where he remained to the time of his death. From 1850 to 1900, scarcely a year passed without some important contribution from Von Koelliker extending the knowledge of histology. His famous text-book on the structure of the tissues (Handbuch der Gewebelehre) passed through six editions from 1852 to 1893, the final edition of it being worked over and brought up to date by this extraordinary man after he had passed the age of seventy-five. By workers in biology this will be recognized as a colossal task. In the second volume of the last edition of this work, which appeared in 1893, he went completely over the ground of the vast accumulation of information regarding the nervous system which an army of gifted and energetic workers had produced. This was all thoroughly digested, and his histological work brought down to date.
Schultze.—The fine observations of Max Schultze (1825-1874) may also be grouped with those of the histologists. We shall have occasion to speak of him more particularly in the chapter on Protoplasm. He did memorable service for general biology in establishing the protoplasm doctrine, but many of his scientific memoirs are in the line of normal histology; as, those on the structure of the olfactory membrane, on the retina of the eye, the muscle elements, the nerves, etc., etc.
Fig. 50.—Von Koelliker, 1817-1905.
Normal Histology and Pathology.—But histology has two phases: the investigation of the tissues in health, which is called normal histology; and the study of the tissues in disease and under abnormal conditions of development, which is designated pathological histology. The latter division, on account of its importance to the medical man, hasbeen extensively cultivated, and the development of pathological study has greatly extended the knowledge of the tissues and has had its influence upon the progress of normal histology. Goodsir, in England, and Henle, in Germany, entered the field of pathological histology, both doing work of historical importance. They were soon followed by Virchow, whose eminence as a man and a scientist has made his name familiar to people in general.
Fig. 51.—Rudolph Virchow, 1821-1903.
Virchow.—Rudolph Virchow (1821-1903), for many years a professor in the University of Berlin, was a notable man in biological science and also as a member of the Germanparliament. He assisted in molding the cell-theory into better form, and in 1858 published a work onCellular Pathology, which applied the cell-theory to diseased tissues. It is to be remembered that Bichat was a medical man, intensely interested in pathological, or diseased, tissues, and we see in Virchow the one who especially extended Bichat's work on the side of abnormal histology. Virchow's name is associated also with the beginning of the idea of germinal continuity, which is the basis of biological ideas regarding heredity (see, further, Chapter XV).
Fig. 52.—Franz Leydig, 1821-1908 (April).Courtesy of Dr. Wm. M. Wheeler.
Leydig.—Franz Leydig (Fig. 52) was early in the field as a histologist with his handbook (Lehrbuch der Histologie des Menschen und der Thiere) published in 1857. He applied histology especially to the tissues of insects in 1864 and subsequent years, an account of which has already been given in Chapter V.
Fig. 53.—S. Ramon y Cajal, 1850-
Cajal as Histologist.—Ramon y Cajal, professor in the University of Madrid, is a histologist whose work in a special field of research is of world-wide renown. His investigations into the microscopic texture of the nervous system and sense-organs have in large part cleared up the questions of the complicated relations between the nervous elements. In company with other European investigators he visited the United States in 1899 on the invitation of Clark University, where his lectures were a feature of the celebration of the tenth anniversary of that university. Besides receiving many honors in previous years, in 1906 he was awarded, in conjunction with the Italian histologist Golgi, one of the Nobel prizes in recognition of his notable investigations. Golgi invented the staining methods that Ramon y Cajal has applied so extensively and so successfully to the histology of the nervous system.
These men in particular may be remembered as the investigators who expanded the work of Bichat on the tissues: Schwann, for disclosing the microscopic elements of animal tissues and founding the cell-theory; Koelliker, as the typical histologist after the analysis of tissues into their elementary parts; Virchow, as extending the cell-idea to abnormal histology; Leydig, for applying histology to the lower animals; and Ramon y Cajal, for investigations into the histology of the nervous system.
Text-Books of Histology.—Besides the works mentioned, the text-books of Frey, Stricker, Ranvier, Klein, Schäfer, and others represent a period in the general introduction of histology to students between 1859 and 1885. But these excellent text-books have been largely superseded by the more recent ones of Stöhr, Boem-Davidoff, Piersol, Szymonowicz, and others. The number of living investigators in histology is enormous; and their work in the subject of cell-structure and in the department of embryology now overlaps.
In pathological histology may be observed an illustration of the application of biological studies to medicine. While no attempt is made to give an account of these practical applications, they are of too great importance to go unmentioned. Histological methods are in constant use in clinical diagnosis, as in blood counts, the study of inflammations, of the action of phagocytes, and of all manner of abnormal growths.
In attempting to trace the beginning of a definite foundation for the work on the structure of tissues, we go back to Bichat rather than to Leeuwenhoek, as Richardson has proposed. Bichat was the first to give a scientific basis for histology founded on extensive observations, since all earlier observers gave only separated accounts of the structure of particular tissues.
CHAPTER IX
THE RISE OF PHYSIOLOGY
Harvey HallerJohannes Müller
Physiologyhad a parallel development with anatomy, but for convenience it will be considered separately. Anatomy shows us that animals and plants are wonderfully constructed, but after we understand their architecture and even their minute structure, the questions remain, What are all the organs and tissues for? and what takes place within the parts that are actually alive? Physiology attempts to answer questions of this nature. It stands, therefore, in contrast with anatomy, and is supplementary to it. The activities of living organisms are varied, and depend on life for their manifestations. These manifestations may be called vital activities. Physiology embraces a study of them all.
Physiology of the Ancients.—This subject began to attract the attention of ancient medical men who wished to fathom the activities of the body in order to heal its diseases, but it is such a difficult thing to begin to comprehend the activities of life that even the simpler relationships were imperfectly understood, and they resorted to mythical explanations. They spoke of spirits and humors in the body as causes of various changes; the arteries were supposed to carry air, the veins only blood; and nothing was known of the circulation. There arose among these early medical men the idea that the body was dominated by a subtle spirit. This went under the namepneuma, and the pneuma-theory held sway until the period of the Revival of Learning.
Among the ancient physiologists the great Roman physician Galen is the most noteworthy figure. As he was the greatest anatomist, so he was also the greatest physiologist of ancient times. All physiological knowledge of the time centered in his writings, and these were the standards of physiology for many centuries, as they were also for anatomy. In the early days anatomy, physiology, and medicine were all united into a poorly digested mass of facts and fancies. This state of affairs lasted until the sixteenth century, and then the awakening came, through the efforts of gifted men, endued with the spirit of independent investigation. The advances made depended upon the work or leadership of these men, and there are certain periods of especial importance for the advance of physiology that must be pointed out.
Period of Harvey.—The first of these epochs to be especially noted here is the period of Harvey (1578-1657). In his time the old idea of spirits and humors was giving way, but there was still much vagueness regarding the activities of the body. He helped to illuminate the subject by showing a connection between arteries and veins, and by demonstrating the circulation of the blood. As we have seen in an earlier chapter, Harvey did not observe the blood passing through the capillaries from arteries to veins, but his reasoning was unassailable that such a connection must exist, and that the blood made a complete circulation. He gave his conclusions in his medical lectures as early as 1619, but did not publish his views until 1628. It was reserved for Malpighi, in 1661, actually to see the circulation through the capillaries under the microscope, and for Leeuwenhoek, in 1669 and later years, to extend these observations.
It was during Harvey's life that the microscope was brought into use and was of such great assistance in advancing knowledge. Harvey himself, however, made little use of this instrument. It was during his life also that the knowledge of development was greatly promoted, first through his own efforts, and later through those of Malpighi.
Harvey is to be recognized, then, as the father of modern physiology. Indeed, before his time physiology as such can hardly be spoken of as having come into existence. He introduced experimental work into physiology, and thus laid the foundation of modern investigation. It was the method of Harvey that made definite progress in this line possible, and accordingly we honor him as one of the greatest as well as the earliest of physiologists.
Period of Haller.—From Harvey's time we pass to the period of Haller (1708-1777), at the beginning of which physiology was still wrapped up with medicine and anatomy. The great work of Haller was to create an independent science of physiology. He made it a subject to be studied for its own sake, and not merely as an adjunct to medicine. Haller was a man of vast and varied learning, and to him was applied by unsympathetic critics the title of "that abyss of learning." His portrait, as shown in Fig. 54, gives the impression of a somewhat pompous and overbearing personality. He was egotistical, self-complacent, and possessed of great self-esteem. The assurance in the inerrancy of his own conclusions was a marked characteristic of Haller's mind. While he was a good observer, his own work showing conscientious care in observation, he was not a good interpreter, and we are to recollect that he vigorously opposed the idea of development set forth by Wolff, and we must also recognize that his researches formed the chief starting-point of an erroneous conception of vitality.
As Verworn points out, Haller's own experiments upon the phenomena of irritability were exact, but they were misinterpreted by his followers, and through the molding influence of others the attempted explanation of their meaning grew into the conception of a special vital force belonging to living organisms only. In its most complete form, this idea provided for a distinct dualism between living and lifeless matter, making all vital actions dependent upon the operation of a mystical supernatural agency. This assumption removed vital phenomena from the domain of clear scientific analysis, and for a long time exercised a retarding influence upon the progress of physiology.
His chief service of permanent value was that he brought into one work all the facts and the chief theories of physiology carefully arranged and digested. This, as has been said, made physiology an independent branch of science, to be pursued for itself and not merely as an adjunct to the study of medicine. The work referred to is his Elements of Physiology (Elementa Physiologiæ Corporis Humani, 1758), one of the noteworthy books marking a distinct epoch in the progress of science.
Fig. 54.—Albrecht Haller, 1708-1777.
To the period of Haller also belongs the discovery of oxygen, in 1774, by Priestley, a discovery which was destined to have profound influence upon the subsequent development of physiology, so that even now physiology consists largely in tracing the way in which oxygen enters the body, the manner in which it is distributed to the tissues, and the various phases of vital activity that it brings about within the living tissues.
Charles Bell.—The period of Haller may be considered as extending beyond his lifetime and as terminating when the influence of Müller began to be felt. Another discovery coming in the closing years of Haller's period marks a capital advance in physiology. I refer to the discovery of Charles Bell (1774-1842) showing that the nerve fibers of the anterior roots of the spinal cord belong to the motor type, while those of the posterior roots belong to the sensory type.
This great truth was arrived at theoretically, rather than as the result of experimental demonstration. It was first expounded by Bell in 1811 in a small essay entitledIdea of a New Anatomy of the Brain, which was printed for private distribution. It was expanded in his papers, beginning in 1821, and published in the Philosophical Transactions of the Royal Society of London, and finally embodied in his work on the nervous system, published in 1830. At this latter date Johannes Müller had reached the age of twenty-nine, and had already entered upon his career as the leading physiologist of Germany. What Bell had divined he demonstrated by experiments.
Charles Bell (Fig. 55) was a surgeon of eminence; in private life he was distinguished by "unpretending amenity, and simplicity of manners and deportment."
Fig. 55.—Charles Bell, 1774-1842.
Period of Johannes Müller.—The period that marks the beginning of modern physiology came next, and was due to the genius and force of Johannes Müller (1801-1858). Verworn says of him: "He is one of those monumental figures that the history of every science brings forth but once.They change the whole aspect of the field in which they work, and all later growth is influenced by their labors." Johannes Müller was a man of very unusual talent and attainments, the possessor of a master mind. Some have said, and not without reason, that there was something supernatural about Müller, for his whole appearance bore the stamp of the uncommon. His portrait, with its massive head above the broad shoulders, is shown in Fig. 56. In his lectures his manner and his gestures reminded one of a Catholic priest. Early in his life, before the disposition to devote himself to science became so overwhelming, he thought of entering the priesthood, and there clung to him all his life some marks of the holy profession. In his highly intellectual face we find "a trace of severity in his mouth and compressed lips, with the expression of most earnest thought on his brow and eyes, and with the remembrance of a finished work in every wrinkle of his countenance."
This extraordinary man exercised a profound influence upon those who came into contact with him. He excited almost unbounded enthusiasm and great veneration among his students. They were allowed to work close by his side, and so magnetic was his personality that he stimulated them powerfully and succeeded in transmitting to them some of his own mental qualities. As professor of physiology in Berlin, Müller trained many gifted young men, among whom were Ludwig (1816-1895), Du Bois-Reymond (1818-1896), and Helmholtz (1821-1894), who became distinguished scholars and professors in German universities. Helmholtz, speaking of Müller's influence on students, paid this tribute to the grandeur of his teacher: "Whoever comes into contact with men of the first rank has an altered scale of values in life. Such intellectual contact is the most interesting event that life can offer."
The particular service of Johannes Müller to science wasto make physiology broadly comparative. So comprehensive was his grasp upon the subject that he gained for himself the title of the greatest physiologist of modern times. He brought together in his great work on the physiology of man not only all that had been previously made known, carefully sifted and digested, but a great mass of new information, which was the result of his own investigations and of those of his students. So rigorous were his scientific standards that he did not admit into this treatise anything which had been untested either by himself or by some of his assistants or students. Verworn says of this monumental work, which appeared in 1833, under the titleHandbuch der Physiologie des Menschen: "This work stands to-day unsurpassed in the genuinely philosophical manner in which the material, swollen to vast proportions by innumerable special researches, was for the first time sifted and elaborated into a unitary picture of the mechanism within the living organism. In this respect theHandbuchis to-day not only unsurpassed, but unequalled."
Müller was the most accurate of observers; indeed, he is the most conspicuous example in the nineteenth century of a man who accomplished a prodigious amount of work all of which was of the highest quality. In physiology he stood on broader lines than had ever been used before. He employed every means at his command—experimenting, the observation of simple animals, the microscope, the discoveries in physics, in chemistry, and in psychology.
He also introduced into physiology the principles of psychology, and it is from the period of Johannes Müller that we are to associate recognition of the close connection between the operations of the mind and the physiology of the brain that has come to occupy such a conspicuous position at the present time.
Fig. 56.—Johannes Müller, 1801-1858.
Müller died in 1858, having reached the age of fifty-seven,but his influence was prolonged through the teachings of his students.
Physiology after Müller
Fig. 57.—Ludwig, 1816-1895.
Ludwig.—Among the men who handed on the torch of Müller there has already been mentioned Ludwig (Fig. 57). For many years he lectured in the University of Leipsic, attracting to that university high-minded, eager,and gifted young men, who received from this great luminary of physiology by expression what he himself had derived from contact with Müller. There are to-day distributed through the universities a number of young physiologists who stand only one generation removed from Johannes Müller, and who still labor in the spirit that was introduced into this department of study by that great master.
Fig. 58.—Du Bois-Reymond, 1818-1896.
Du Bois-Reymond.—Du Bois-Reymond (Fig. 58), another of his distinguished pupils, came to occupy the chairwhich Müller himself had filled in the University of Berlin, and during the period of his vigor was in physiology one of the lights of the world. It is no uncommon thing to find recently published physiologies dedicated either to the memory of Johannes Müller, as in the case of that remarkableGeneral Physiologyby Verworn; or to Ludwig, or to Du Bois-Reymond, who were in part his intellectual product. From this disposition among physiologists to do homage to Müller, we are able to estimate somewhat more closely the tremendous reach of his influence.
Bernard.—When Müller was twelve years old there was born in Saint-Julien, department of the Rhône, Claude Bernard, who attained an eminence as a physiologist, of which the French nation are justly proud. Although he was little thought of as a student, nevertheless after he came under the influence of Magendie, at the age of twenty-six, he developed rapidly and showed his true metal. He exhibited great manual dexterity in performing experiments, and also a luminous quality of mind in interpreting his observations. One of his greatest achievements in physiology was the discovery of the formation within the liver of glycogen, a substance chemically related to sugar. Later he discovered the system of vaso-motor nerves that control and regulate the caliber of the blood-vessels. Both of these discoveries assisted materially in understanding the wonderful changes that are going on within the human body. But besides his technical researches, any special consideration of which lies quite beyond the purpose of this book, he published in 1878-1879 a work upon the phenomena of life in animals and vegetables, a work that had general influence in extending the knowledge of vital activities. I refer to his now classicLeçons sur les Phénomènes de la vie communs aux animaux et aux végétaux.
The thoughtful face of Bernard is shown in his portrait,Fig. 59. He was one of those retiring, silent men whose natures are difficult to fathom, and who are so frequently misunderstood. A domestic infelicity, that led to the separation of himself from his family, added to his isolation and loneliness. When touched by the social spirit he charmed people by his personality. He was admired by the Emperor Napoleon Third, through whose influence Bernard acquired two fine laboratories. In 1868 he was elected to the French Academy, and became thereby one of the "Forty Immortals."
Fig. 59.—Claude Bernard, 1813-1878.
Foster describes him thus: "Tall in stature, with a finepresence, with a noble head, the eyes full at once of thought and kindness, he drew the look of observers upon him wherever he appeared. As he walked in the streets passers-by might be heard to say 'I wonder who that is; he must be some distinguished man.'"
Two Directions of Growth.—Physiology, established on the broad foundations of Müller, developed along two independent pathways, the physical and the chemical. We find a group of physiologists, among whom Weber, Ludwig, Du Bois-Reymond, and Helmholtz were noteworthy leaders, devoted to the investigations of physiological facts through the application of measurements and records made by machinery. With these men came into use the time-markers, the myographs, and the ingenious methods of recording blood-pressure, changes in respiration, the responses of muscle and nerve to various forms of stimulation, the rate of transmission of nerve-currents, etc.
The investigation of vital activities by means of measurements and instrumental records has come to represent one especial phase of modern physiology. As might have been predicted, the discoveries and extensions of knowledge resulting from this kind of experimentation have been remarkable, since it is obvious that permanent records made by mechanical devices will rule out many errors; and, moreover, they afford an opportunity to study at leisure phenomena that occupy a very brief time.
The other marked line of physiological investigation has been in the domain of chemistry, where Wöhler, Liebig, Kühne, and others have, through the study of the chemical changes occurring in its body, observed the various activities that take place within the organism. They have reduced all tissues and all parts of the body to chemical analysis, studied the chemical changes in digestion, in respiration, etc. The more recent observers have also made a particular feature ofthe study of the chemical changes going on within the living matter.
The union of these two chief tendencies into the physico-chemical aspects of physiology has established the modern way of looking upon vital activities. These vital activities are now regarded as being, in their ultimate analysis, due to physical and chemical changes taking place within the living substratum. All along, this physico-chemical idea has been in contest with that of a duality between the body and the life that is manifested in it. The vitalists, then, have had many controversies with those who make their interpretations along physico-chemical lines. We will recollect that vitalism in the hands of the immediate successors of Haller became not only highly speculative, but highly mystical, tending to obscure any close analysis of vital activity and throwing explanations all back into the domain of mysticism. Johannes Müller was also a vitalist, but his vitalism was of a more acceptable form. He thought of changes in the body as being due to vitality—to a living force; but he did not deny the possibility of the transformation of this vital energy into other forms of energy; and upon the basis of Müller's work there has been built up the modern conception that there is found in the human body a particular transformation-form of energy, not a mystical vital force that presides over all manifestations of life.
The advances in physiology, beginning with those of William Harvey, have had immense influence not only upon medicine, but upon all biology. We find now the successful and happy union between physiology and morphology in the work which is being so assiduously carried on to-day under the title of experimental morphology.
The great names in physiology since Müller are numerous, and perhaps it is invidious to mention particular ones; but, inasmuch as Ludwig and Du Bois-Reymond have beenspoken of, we may associate with them the names of Sir Michael Foster and Burdon-Sanderson, in England; and of Brücke (one of Müller's disciples) and Verworn, in Germany, as modern leaders whose investigations have promoted advance, and whose clear exposition of the facts and the theories of physiology have added much to the dignity of the science.
CHAPTER X
VON BAER AND THE RISE OF EMBRYOLOGY
Anatomyinvestigates the arrangement of organic tissues; embryology, or the science of development, shows how they are produced and arranged. There is no more fascinating division of biological study. As Minot says: "Indeed, the stories which embryology has to tell are the most romantic known to us, and the wildest imaginative creations of Scott or Dumas are less startling than the innumerable and almost incredible shifts of rôle and change of character which embryology has to entertain us with in her histories."
Embryology is one of the most important biological sciences in furnishing clues to the past history of animals. Every organism above the very lowest, no matter how complex, begins its existence as a single microscopic cell, and between that simple state and the fully formed condition every gradation of structure is exhibited. Every time an animal is developed these constructive changes are repeated in orderly sequence, and one who studies the series of steps in development is led to recognize that the process of building an animal's body is one of the most wonderful in all nature.
Rudimentary Organs.—But, strangely enough, the course of development in any higher organism is not straightforward, but devious. Instead of organs being produced in the most direct manner, unexpected by-paths are followed, as when all higher animals acquire gill-clefts and many other rudimentary organs not adapted to their condition of life. Most of the rudimentary organs are transitory, and bear testimony, as hereditary survivals, to the line of ancestry. They are clues by means of which phases in the evolution of animal life may be deciphered.
Bearing in mind the continually shifting changes through which animals pass in their embryonic development, one begins to see why the adult structures of animals are so difficult to understand. They are not only complex; they are also greatly modified. The adult condition of any organ or tissue is the last step in a series of gradually acquired modifications, and is, therefore, the farthest departure from that which is ancestral and archetypal. But in the process of formation all the simpler conditions are exhibited. If, therefore, we wish to understand an organ or an animal, we must follow its development, and see it in simpler conditions, before the great modifications have been added.
The tracing of the stages whereby cells merge into tissues, tissues into organs, and determining how the organs by combinations build up the body, is embryology. On account of the extended applications of this subject in biology, and the light which it throws on all structural studies, we shall be justified in giving its history at somewhat greater length than that adopted in treating of other topics.
Five Historical Periods.—The story of the rise of this interesting department of biology can, for convenience, be divided into five periods, each marked by an advance in general knowledge. These are: (1) the period of Harvey and Malpighi; (2) the period of Wolff; (3) the period of Von Baer; (4) the period from Von Baer to Balfour; and (5) the period of Balfour, with an indication of present tendencies. Among all the leaders Von Baer stands as a monumental figure at the parting of the ways between the new and the old—the sane thinker, the great observer.
The Period of Harvey and Malpighi
In General.—The usual account of the rise of embryology is derived from German writers. But there is reason to depart from their traditions, in which Wolff is heralded as its founder, and the one central figure prior to Pander and Von Baer.
The embryological work of Wolff's great predecessors, Harvey and Malpighi, has been passed over too lightly. Although these men have received ample recognition in closely related fields of investigation, their insight into those mysterious events that culminate in the formation of a new animal has been rarely appreciated. Now and then a few writers, as Brooks and Whitman, have pointed out the great worth of Harvey's work in embryology, but fewer have spoken for Malpighi in this connection. Koelliker, it is true, in his address at the unveiling of the statue of Malpighi, in his native town of Crevalcuore, in 1894, gives him well-merited recognition as the founder of embryology, and the late Sir Michael Foster has written in a similar vein in his delightfulLectures on the History of Physiology.
However great was Harvey's work in embryology, I venture to say that Malpighi's was greater when considered as a piece of observation. Harvey's work is more philosophical; he discusses the nature of development, and shows unusual powers as an accurate reasoner. But that part of his treatise devoted to observation is far less extensive and exact than Malpighi's, and throughout his lengthy discussions he has the flavor of the ancients.
Malpighi's work, on the contrary, flavors more of the moderns. In terse descriptions, and with many sketches, he shows the changes in the hen's egg from the close of the first day of development onward.
It is a noteworthy fact that, at the period in which helived, Malpighi could so successfully curb the tendency to indulge in wordy disquisitions, and that he was satisfied to observe carefully, and tell his story in a simple way. This quality of mind is rare. As Emerson has said: "I am impressed with the fact that the greatest thing a human soul ever does in this world is to see something, and tell what it saw in a plain way. Hundreds of people can talk for one who can think, but thousands can think for one who can see. To see clearly is poetry, philosophy, and religion all in one." But "to see" here means, of course, to interpret as well as to observe.
Although there were observers in the field of embryology before Harvey, little of substantial value had been produced. The earliest attempts were vague and uncritical, embracing only fragmentary views of the more obvious features of body-formation. Nor, indeed, should we look for much advance in the field of embryology even in Harvey's time. The reason for this will become obvious when we remember that the renewal of independent observation had just been brought about in the preceding century by Vesalius, and that Harvey himself was one of the pioneers in the intellectual awakening. Studies on the development of the body are specialized, involving observations on minute structures and recondite processes, and must, therefore, wait upon considerable advances in anatomy and physiology. Accordingly, the science of embryology was of late development.
Harvey.—Harvey's was the first attempt to make a critical analysis of the process of development, and that he did not attain more was not owing to limitations of his powers of discernment, but to the necessity of building on the general level of the science of his time, and, further, to his lack of instruments of observation and technique. Nevertheless, Harvey may be considered as having made the first independent advance in embryology.
By clearly teaching, on the basis of his own observations, the gradual formation of the body by aggregation of its parts, he anticipated Wolff. This doctrine came to be known under the title of "epigenesis," but Harvey's epigenesis[3]was not, as Wolff's was, directed against a theory of pre-delineation of the parts of the embryo, but against the ideas of the medical men of the time regarding the metamorphosis of germinal elements. It lacked, therefore, the dramatic setting which surrounded the work of Wolff in the next century. Had the doctrine of pre-formation been current in Harvey's time, we are quite justified in assuming that he would have assailed it as vigorously as did Wolff.
His Treatise on Generation.—Harvey's embryological work was published in 1651 under the titleExercitationes de Generatione Animalium. It embraces not only observations on the development of the chick, but also on the deer and some other mammals. As he was the court physician of Charles I, that sovereign had many deer killed in the park, at intervals, in order to give Harvey the opportunity to study their development.
As fruits of his observation on the chick, he showed the position in which the embryo arises within the egg,viz., in the white opaque spot or cicatricula; and he also corrected Aristotle, Fabricius, and his other predecessors in many particulars.
Harvey's greatest predecessor in this field, Fabricius, was also his teacher. When, in search of the best training in medicine, Harvey took his way from England to Italy, as already recounted, he came under the instruction of Fabricius in Padua. In 1600, Fabricius published sketches showing the development of animals; and, again, in 1625, six years after his death, appeared his illustrated treatise onthe development of the chick. Except the figures of Coiter (1573), those of Fabricius were the earliest published illustrations of the kind. Altogether his figures show developmental stages of the cow, sheep, pig, galeus, serpent, rat, and chick.
Harvey's own treatise was not illustrated. With that singular independence of mind for which he was conspicuous, the vision of the pupil was not hampered by the authority of his teacher, and, trusting only to his own sure observation and reason, he described the stages of development as he saw them in the egg, and placed his own construction on the facts.
One of the earliest activities to arrest his attention in the chick was a pulsating point, the heart, and, from this observation, he supposed that the heart and the blood were the first formations. He says: "But as soon as the egg, under the influence of the gentle warmth of the incubating hen, or of warmth derived from another source, begins to pullulate, this spot forthwith dilates, and expands like the pupil of the eye; and from thence, as the grand center of the egg, the latent plastic force breaks forth and germinates. This first commencement of the chick, however, so far as I am aware, has not yet been observed by any one."
It is to be understood, however, that the descriptive part of his treatise is relatively brief (about 40 pages out of 350 in Willis's translation), and that the bulk of the 106 "exercises" into which his work is divided is devoted to comments on the older writers and to discussions of the nature of the process of development.
The aphorism, "omne vivum ex ovo," though not invented by Harvey, was brought into general use through his writings. As used in his day, however, it did not have its full modern significance. With Harvey it meant simply that the embryos of all animals, the viviparous as well as the oviparous,originate in eggs, and it was directed against certain contrary medical theories of the time.
Fig. 60.—Frontispiece to Harvey'sGeneratione Animalium(1651).
The first edition of hisGeneratione Animalium, London, 1651, is provided with an allegorical frontispiece embodying this idea. As shown in Fig. 60, it represents Jove on a pedestal, uncovering a round box, or ovum, bearing the inscription "ex ovo omnia," and from the box issue all forms of living creatures, including also man.
Malpighi.—The observer in embryology who looms into prominence between Harvey and Wolff is Malpighi. He supplied what was greatly needed at the time—an illustrated account of the actual stages in the development of the chick from the end of the first day to hatching, shorn of verbose references and speculations.
His observations on development are in two separate memoirs, both sent to the Royal Society in 1672, and published by the Society in Latin, under the titlesDe Formatione Pulli in OvoandDe Ovo Incubato. The two taken together are illustrated by twelve plates containing eighty-six figures, and the twenty-two quarto pages of text are nearly all devoted to descriptions, a marked contrast to the 350 pages of Harvey unprovided with illustrations.
His pictures, although not correct in all particulars, represent what he was able to see, and are very remarkable for the age in which they were made, and considering the instruments of observation at his command. They show successive stages from the time the embryo is first outlined, and, taken in their entirety, they cover a wide range of stages.
His observations on the development of the heart, comprising twenty figures, are the most complete. He clearly illustrates the aortic arches, those transitory structures of such great interest as showing a phase in ancestral history.
Fig. 61.—Selected Sketches from Malpighi's Works. Showing Stages in the Development of the Chick (1672).
He was also the first to show by pictures the formation of the head-fold and the neural groove, as well as the brain-vesicles and eye-pockets. His delineation of heart, brain, and eye-vesicles are far ahead of those illustrating Wolff'sTheoria Generationis, made nearly a hundred years later.
Fig. 61 shows a few selected sketches from the various plates of his embryological treatises, to compare with those of Wolff. (See Fig. 63.)