Authorities.—A. Daux,Recherches sur l’origine et l’emplacement des emporia phéniciens dans le Zeugis et le Byzacium(Paris, 1869); Ch. Tissot,Géographie comparée de la province romaine d’Afrique, ii. p. 149; Cagnat,Explorations archéol. en Tunisie(2nd and 3rd fasc., 1885); Lud. Müller,Numismatique de l’Afrique ancienne, ii p. 51; M. Palat, in theBulletin arch. du Comité des travaux historiques(1885), pp. 121 and 150;Revue archéologique(1884 and 1897);Bulletin des antiquités africaines(1884 and 1885);Bulletin de la Société archéologique de Sousse(first published in 1903);Atlas archéol. de Tunisie(4th fascicule, with the plan of Hadrumetum).
Authorities.—A. Daux,Recherches sur l’origine et l’emplacement des emporia phéniciens dans le Zeugis et le Byzacium(Paris, 1869); Ch. Tissot,Géographie comparée de la province romaine d’Afrique, ii. p. 149; Cagnat,Explorations archéol. en Tunisie(2nd and 3rd fasc., 1885); Lud. Müller,Numismatique de l’Afrique ancienne, ii p. 51; M. Palat, in theBulletin arch. du Comité des travaux historiques(1885), pp. 121 and 150;Revue archéologique(1884 and 1897);Bulletin des antiquités africaines(1884 and 1885);Bulletin de la Société archéologique de Sousse(first published in 1903);Atlas archéol. de Tunisie(4th fascicule, with the plan of Hadrumetum).
(E. B.*)
HAECKEL, ERNST HEINRICH(1834-  ), German biologist, was born at Potsdam on the 16th of February 1834. He studied medicine and science at Würzburg, Berlin and Vienna, having for his masters such men as Johannes Müller, R. Virchow and R. A. Kölliker, and in 1857 graduated at Berlin as M.D. and M.Ch. At the wish of his father he began to practise as a doctor in that city, but his patients were few in number, one reason being that he did not wish them to be many, and after a short time he turned to more congenial pursuits. In 1861, at the instance of Carl Gegenbaur, he becamePrivatdozentat Jena; in the succeeding year he was chosen extraordinary professor of comparative anatomy and director of the Zoological Institute in the same university; in 1865 he was appointed to a chair of zoology which was specially established for his benefit. This last position he retained for 43 years, in spite of repeated invitations to migrate to more important centres, such as Strassburg or Vienna, and at Jena he spent his life, with the exception of the time he devoted to travelling in various parts of the world, whence in every case he brought back a rich zoological harvest.
As a field naturalist Haeckel displayed extraordinary power and industry. Among his monographs may be mentioned those onRadiolaria(1862),Siphonophora(1869),Monera(1870) andCalcareous Sponges(1872), as well as severalChallengerreports, viz.Deep-Sea Medusae(1881),Siphonophora(1888),Deep-Sea Keratosa(1889) andRadiolaria(1887), the last being accompanied by 140 plates and enumerating over four thousand new species. This output of systematic and descriptive work would alone have constituted a good life’s work, but Haeckel in addition wrote copiously on biological theory. It happened that just when he was beginning his scientific career Darwin’sOrigin of Specieswas published (1859), and such was the influence it exercised over him that he became the apostle of Darwinism in Germany. He was, indeed, the first German biologist to give a whole-hearted adherence to the doctrine of organic evolution and to treat it as the cardinal conception of modern biology. It was he who first brought it prominently before the notice of German men of science in his first memoir on theRadiolaria, which was completely pervaded with its spirit, and later at the congress of naturalists at Stettin in 1863. Darwin himself has placed on record the conviction that Haeckel’s enthusiastic propagandism of the doctrine was the chief factor of its success in Germany. His book onGeneral Morphology(1866), published when he was only thirty-two years old, was called by Huxley a suggestive attempt to work out the practical application of evolution to its final results; and if it does not take rank as a classic, it will at least stand out as a landmark in the history of biological doctrine in the 19th century. Although it contains a statement of most of the views with which Haeckel’s name is associated, it did not attract much attention on its first appearance, and accordingly its author rewrote much of its substance in a more popular style and published it a year or two later as theNatural History of Creation(Natürliche Schöpfungsgeschichte), which was far more successful. In it he divided morphology into two sections—tectology, the science of organic individuality; and promorphology, which aims at establishing a crystallography of organic forms. Among other matters, he laid particular stress on the “fundamental biogenetic law†that ontogeny recapitulates phylogeny, that the individual organism in its development is to a great extent an epitome of the form-modifications undergone by the successive ancestors of the species in the course of their historic evolution. His well-known “gastraea†theory is an outcome of this generalization. He divided the whole animal creation into two categories—the Protozoa or unicellular animals, and the Metazoa or multicellular animals, and he pointed out that while the former remain single-celled throughout their existence, the latter are only so at the beginning, and are subsequently built up of innumerable cells, the single primitive egg-cell (ovum) being transformed by cleavage into a globular mass of cells (morula), which first becomes a hollow vesicle and then changes into thegastrula. The simplest multicellular animal he conceived to resemble this gastrula with its two primary layers, ectoderm and endoderm, and the earliest hypothetical form of this kind, from which the higher animals might be supposed to be actually descended, he called the “gastraea.†This theory was first put forward in the memoir on the calcareous sponges, which in its sub-title was described as an attempt at an analytical solution of the problem of the origin of species, and was subsequently elaborated in variousStudies on the Gastraea Theory(1873-1884). Haeckel, again, was the first to attempt to draw up a genealogical tree (Stammbaum) exhibiting the relationship between the various orders of animalswith regard both to one another and their common origin. His earliest attempt in theGeneral Morphologywas succeeded by many others, and his efforts in this direction may perhaps be held to culminate in the paper he read before the fourth International Zoological Congress, held at Cambridge in 1898, when he traced the descent of the human race in twenty-six stages from organisms like the still-existingMonera, simple structureless masses of protoplasm, and the unicellularProtista, through the chimpanzees and thePithecanthropus erectus, of which a few fossil bones were discovered in Java in 1894, and which he held to be undoubtedly an intermediate form connecting primitive man with the anthropoid apes.
Not content with the study of the doctrine of evolution in its zoological aspects, Haeckel also applied it to some of the oldest problems of philosophy and religion. What he termed the integration of his views on these subjects he published under the title ofDie Welträtsel(1899), which in 1901 appeared in English asThe Riddle of the Universe. In this book, adopting an uncompromising monistic attitude, he asserted the essential unity of organic and inorganic nature. According to his “carbon-theory,†which has been far from achieving general acceptance, the chemico-physical properties of carbon in its complex albuminoid compounds are the sole and the mechanical cause of the specific phenomena of movement which distinguish organic from inorganic substances, and the first development of living protoplasm, as seen in theMonera, arises from such nitrogenous carbon-compounds by a process of spontaneous generation. Psychology he regarded as merely a branch of physiology, and psychical activity as a group of vital phenomena which depend solely on physiological actions and material changes taking place in the protoplasm of the organism in which it is manifested. Every living cell has psychic properties, and the psychic life of multicellular organisms is the sum-total of the psychic functions of the cells of which they are composed. Moreover, just as the highest animals have been evolved from the simplest forms of life, so the highest faculties of the human mind have been evolved from the soul of the brute-beasts, and more remotely from the simple cell-soul of the unicellular Protozoa. As a consequence of these views Haeckel was led to deny the immortality of the soul, the freedom of the will, and the existence of a personal God.
Haeckel’s literary output was enormous, and at the time of the celebration of his sixtieth birthday at Jena in 1894 he had produced 42 works with 13,000 pages, besides numerous scientific memoirs. In addition to the works already mentioned, he wroteFreie Wissenschaft und freie Lehre(1877) in reply to a speech in which Virchow objected to the teaching of the doctrine of evolution in schools, on the ground that it was an unproved hypothesis;Die systematische Phylogenie(1894), which has been pronounced his best book;Anthropogenie(1874, 5th and enlarged edition 1903), dealing with the evolution of man;Über unsere gegenwärtige Kenntnis vom Ursprung des Menschen(1898, translated into English asThe Last Link, 1898);Der Kampf um den Entwickelungsgedanken(1905, English version,Last Words on Evolution, 1906);Die Lebenswunder(1904), a supplement to theRiddle of the Universe; books of travel, such asIndische Reisebriefe(1882) andAus Insulinde(1901), the fruits of journeys to Ceylon and to Java;Kunstformen der Natur(1904), with plates representing beautiful marine animal forms; andWanderbilder(1905), reproductions of his oil-paintings and water-colour landscapes.
There are biographies by W. Bölsche (Dresden, 1900, translated into English by Joseph McCabe, with additions, London, 1906) and by Breitenbach (Odenkirchen, 1904). See also Walther May,Ernst Haeckel;Versuch einer Chronik seines Lebens und Werkens(Leipzig, 1909).
There are biographies by W. Bölsche (Dresden, 1900, translated into English by Joseph McCabe, with additions, London, 1906) and by Breitenbach (Odenkirchen, 1904). See also Walther May,Ernst Haeckel;Versuch einer Chronik seines Lebens und Werkens(Leipzig, 1909).
HAEMATITE,orHematite, a mineral consisting of ferric oxide (Fe2O3), named from the Greek wordαἷμα“blood,†in allusion to its typical colour, whence it is called also red iron ore. When crystallized, however, haematite often presents a dark colour, even iron-black; but on scratching the surface, the powder of the streak shows the colour of dried blood. Haematite crystallizes in the rhombohedral system, and is isomorphous with corundum (Al2O3). The habit of the crystals may be rhombohedral, pyramidal or tabular, rarely prismatic. In fig. 1 the crystal, from Elba, shows a combination of the fundamental rhombohedron (R), an obtuse rhombohedron (s), and the hexagonal bi-pyramid (n). Fig. 2 is a tabular crystal in which the basal pinacoid (o) predominates. Haematite has no distinct cleavage, but may show, in consequence of a lamellar structure, a tendency to parting along certain planes.
Crystallized haematite, such as that from the iron-mines of Elba, presents a steel-grey or iron-black colour, with a brilliant metallic lustre, sometimes beautifully iridescent. The splendent surface has suggested for this mineral such names as specular iron ore, looking-glass ore, and iron glance (fer oligisteof French writers). The hardness of the crystallized haematite is about 6, and the specific gravity 5.2. The so-called “iron roses†(Eisenrosen) of Switzerland are rosette-like aggregates of hexagonal tabular crystals, from fissures in the gneissose rocks of the Alps. Specular iron ore occurs in the form of brilliant metallic scales on many lavas, as at Vesuvius and Etna, in the Auvergne and the Eifel, and notably in the Island of Ascension, where the mineral forms beautiful tabular crystals. It seems to be a sublimation-product formed in volcanoes by the interaction of the vapour of ferric chloride and steam.
Specular haematite forms a constituent of certain schistose rocks, such as the Brazilian itabirite. In the Marquette district of Michigan (Lake Superior) schistose specular ore occurs in important deposits, associated with a jasper rock, in which the ore alternates with bands of red quartzite. Micaceous iron ore consists of delicate steel-grey scales of specular haematite, unctuous to the touch, used as a lubricant and also as a pigment. It is worked in Devonshire under the name of shining ore. Very thin laminae of haematite, blood-red by transmitted light, occur as microscopic enclosures in certain minerals, such as carnallite and sun-stone, to which they impart colour and lustre.
Much haematite occurs in a compact or massive form, often mammillary, and presenting on fracture a fibrous structure. The reniform masses are known as kidney ore. Such red ore is generally neither so dense nor so hard as the crystals. It often passes into an earthy form, termed soft red ore, and when mixed with more or less clay constitutes red ochre, ruddle or reddle (Ger.Rötel).
The hard haematite is occasionally cut and polished as an ornamental stone, and certain kinds have been made into beads simulating black pearls. It was worked by the Assyrians for their engraved cylinder-seals, and was used by the gnostics for amulets. Some of the native tribes in the Congo basin employ it as a material for axes. The hard fibrous ore of Cumberland is known as pencil ore, and is employed for the burnishers used by bookbinders and others. Santiago de Compostela in Spain furnishes a considerable supply of haematite burnishers.
Haematite is an important ore of iron (q.v.), and is extensively worked in Elba, Spain (Bilbao), Scandinavia, the Lake Superior region and elsewhere. In England valuable deposits occur in the Carboniferous Limestone of west Cumberland (Whitehaven district) and north Lancashire (Ulverston district). The hard ore is siliceous, and fine crystallized specimens occur in association with smoky quartz. The ore is remarkably free from phosphorus, and is consequently valued for the production of pig-iron to be converted into Bessemer steel.
(F. W. R.*)
HAEMATOCELE(Gr.αἷμα, blood, andκήλη, tumour), the medical term for a localized collection of blood in the tunica vaginalis or cord. It is usually the result of a sudden blow or severe strain, but may arise from disease. At first it forms a smooth, fluctuating, opaque swelling, but later becomes hard and firm. In chronic cases the walls of the tunica vaginalisundergo changes. The treatment of a case seen soon after the injury is directed towards keeping the patient at rest, elevating the parts, and applying an evaporating lotion or ice-bag. In chronic cases it may be necessary to lay open the cavity and remove the coagulum.
HAEMOPHILIA,the medical term for a condition of the vascular system, often running in families, the members of which are known as “bleeders,†characterized by a disposition towards bleeding, whether with or without the provocation of an injury to the tissue. When this bleeding is spontaneous it comes from the mucous membranes, especially from the nose, but also from the mouth, bowel and bronchial tubes. Slight bruises are apt to be followed by extravasations of blood into the tissues; the swollen joints (knee especially) of a bleeder are probably due, in the first instance, to the escape of blood into the joint cavity or synovial membrane. It is always from the smallest vessels that the blood escapes, and may do so in such quantities as to cause death in a few hours.
HAEMORRHAGE(Gr.αἷμα, blood, andῥηγνÏναι, to burst), a general term for any escape of blood from a blood-vessel (see Blood). It commonly results from injury, as the tearing or cutting of a blood-vessel, but certain forms result from disease, as in scurvy and purpura. The chief varieties of haemorrhage arearterial,venousandcapillary. Bleeding from an artery is of a bright red colour, and escapes from the end of the vessel nearest the heart in jets synchronous with the heart’s beat. Bleeding from a vein is of a darker colour; the flow is steady, and the bleeding is from the distal end of the vessel. Capillary bleeding is a general oozing from a raw surface. Byextravasation of bloodis meant the pouring out of blood into the areolar tissues, which become boggy. This is termed abruiseorecchymosis.Epistaxisis a term given to bleeding from the nose.Haematemesisis vomiting of blood, the colour of which may be altered by digestion, as is also the case inmelaena, or passage of blood with the faeces, in which the blood becomes dark and tarry-looking from the action of the intestinal fluids.Haemoptysisdenotes an escape of blood from the air-passages, which is usually bright red and frothy from admixture with air.Haematuriameans passage of blood with the urine.
Cessation of bleeding may take place from natural or from artificial means. Natural arrest of haemorrhage arises from (1) the coagulation of the blood itself, (2) the diminution of the heart’s action as in fainting, (3) changes taking place in the cut vessel causing its retraction and contraction. In the surgical treatment of haemorrhage minor means of arresting bleeding are: cold, which is most valuable in general oozing and local extravasations; very hot water, 130° to 160° F., a powerful haemostatic; position, such as elevation of the limb, valuable in bleeding from the extremities; styptics or astringents, applied locally, as perchloride of iron, tannic acid and others, the most valuable being suprarenal extract. In arresting haemorrhage temporarily the chief thing is to press directly on the bleeding part. The pressure to be effectual need not be severe, but must be accurately applied. If the bleeding point cannot be reached, the pressure should be applied to the main artery between the bleeding point and the heart. In small blood-vessels pressure will be sufficient to arrest haemorrhage permanently. In large vessels it is usual to pass a ligature round the vessel and tie it with a reef-knot. Apply the ligature, if possible, at the bleeding point, tying both ends of the cut vessel. If this cannot be done, the main artery of the limb must be exposed by dissection at the most accessible point between the wound and the heart, and there ligatured.
Haemorrhage has been classified as—(1) primary, occurring at the time of the injury; (2) reactionary, or within twenty-four hours of the accident, during the stage of reaction; (3) secondary, occurring at a later period and caused by faulty application of a ligature or septic condition of the wound. In severe haemorrhage, as from the division of a large artery, the patient may collapse and death ensue from syncope. In this case stimulants and strychnine may be given, but they should be avoided until it is certain the bleeding has been properly controlled, as they tend to increase it. Transfusion of blood directly from the vein of a healthy person to the blood-vessels of the patient, and infusion of saline solution into a vein, may be practised (see Shock). In a congenital condition known ashaemophylia(q.v.) it is difficult to stop the flow of blood.
The surgical procedure for the treatment of an open wound is—(1) arrest of haemorrhage; (2) cleansing of the wound and removal of any foreign bodies; (3) careful apposition of its edges and surfaces—the edges being best brought in contact by sutures of aseptic silk or catgut, the surfaces by carefully applied pressure; (4) free drainage, if necessary, to prevent accumulation either of blood or serous effusion; (5) avoidance of sepsis; (6) perfect rest of the part. These methods of treatment require to be modified for wounds in special situations and for those in which there is much contusion and laceration. When a special poison has entered the wound at the time of its infliction or at some subsequent date, it is necessary to provide against septic conditions of the wound itself and blood-poisoning of the general circulation.
HAEMORRHOIDS,or Hemorrhoids (from Gr.αἷμα, blood, andῥεῖν, to flow), commonly calledpiles, swellings formed by the dilatation of veins of the lowest part of the bowel, or of those just outside the margin of its aperture. The former,internal piles, are covered by mucous membrane; the latter,external piles, are just beneath the skin. As the veins of the lining of the bowel become dilated they form definite bulgings within the bowel, and, at last increasing in size, escape through the anus when a motion is being passed. Growing still larger, they may come down spontaneously when the individual is standing or walking, and they are apt to be a grave source of pain or annoyance. Eventually they may remain constantly protruded—nevertheless, they are stillinternalpiles because they arise from the interior of the bowel. Though a pile is sometimes solitary, there are usually several of them. They are apt to become inflamed, and the inflammation is associated with heat, pain, discharge and general uneasiness; ulceration and bleeding are also common symptoms, hence the term “bleeding piles.†Theexternal pileis covered by the thin dark-coloured skin of the anal margin. Severe pressure upon the large abdominal veins may retard the upward flow of blood to the heart and so give rise to piles; this is apt to happen in the case of disease of the liver, malignant and other tumours, and pregnancy. General weakness of the constitution or of the blood-vessels and habitual constipation may be predisposing causes of piles. The exciting cause may be vigorous straining at stool or exposure to damp, as from sitting on the wet ground. Piles are often only a symptom, and in their treatment this fact should be kept in view; if the cause is removed the piles may disappear. But in some cases it may be impossible to remove the cause, as when a widely-spreading cancerous growth of the rectum, or of the interior of the pelvis or abdomen, is blocking the upward flow of blood in the veins. Sometimes when a pile has been protruded, as during defaecation, it is tightly grasped by spasmodic contraction of the circular muscular fibres which guard the outlet of the bowel, and it then becomes swollen, engorged and extremely painful; the strangulation may be so severe that the blood in the vessels coagulates and the pile mortifies. This, indeed, is nature’s attempt at curing a pile, but it is distressing, and, as a rule, it is not entirely successful.
The palliative treatment of piles consists in obtaining a daily and easy action of the bowels, in rest, cold bathing, astringent injections, lotions and ointments. The radical treatment consists in their removal by operation, but this should not be contemplated until palliative treatment has failed. The operation consists in drawing the pile well down, and strangling the vessels entering and leaving its base, either by a strong ligature tightly applied, by crushing, or by cautery. Before dealing with the pile the anus is vigorously dilated in order that the pile may be dealt with with greater precision, and also that the temporary paralysis of the sphincter muscle, which follows the stretching, may prevent the occurrence of painful and spasmodic contractions subsequently. The ligatures by which the base of the piles are strangulatedslough off with the pile in about ten days, and in about ten days more the individual is, as a rule, well enough to return to his work. If, for one reason or another, no operation is to be undertaken, and the piles are troublesome, relief may be afforded by warm sponging and by sitz-baths, the pile being gently dried afterwards by a piece of soft linen, smeared with vaseline, and carefully returned into the bowel. Under surgical advice, cocaine or morphia may be brought in contact with the tender parts, either in the form of lotion, suppository or ointment. In operating upon internal piles it is undesirable to remove all the external piles around the anus, lest the contraction of the circumferential scar should cause permanent narrowing of the orifice. If, as often happens, blood clots in the vein of an external pile, the small, hard, tender swelling may be treated with anodyne fomentations, or it may be rendered insensitive by the ether spray and opened by a small incision, the clot being turned out.
(E. O.*)
HAEMOSPORIDIA,in zoology, an order of Ectospora, which although comparatively few in number and very inconspicuous in size and appearance, have of late years probably attracted greater attention and been more generally studied than any other Sporozoa; the reason being that they include the organisms well known as malarial parasites. In spite, however, of much and careful recent research—to a certain extent, rather, as a result of it—it remains the case that the Haemosporidia are, in some respects, the group of the Ectospora about which our knowledge is, for the time being, in the most unsatisfactory condition. Such important questions, indeed, as the scope and boundaries of the group, its exact origin and affinities, the rank and interclassification of the forms admittedly included in it, are answered quite differently by different workers. For example, one well-known Sporozoan authority (M. Lühe) has recently united the two groups, Haemosporidia and Haemoflagellates, bodily into one, while others (e.g.Novy and McNeal) deny that there is any connexion whatever between “Cytozoa†and Trypanosomes. Again, the inclusion or exclusion of forms likePiroplasmaandHalteridiumis also the subject of much discussion. The present writer accepts here the view that the Haemosporidia are derived from Haemoflagellates which have developed a gregariniform (Sporozoan) phase at the expense, largely or entirely, of the flagelliform one. The not inconsiderable differences met with among different types are capable of explanation on the ground that certain forms have advanced farther than others along this particular line of evolution. In other words, it is most probable that the Haemosporidia are to be regarded as comprising various parasites which represent different stages intermediate between, on the one side, a Flagellate, and on the other, a typical chlamydospore-forming Ectosporan parasite. While, however, it is easy enough sharply to separate off all Haemosporidia from other Ectospora, it is a very difficult matter to define their limits on the former side. Two principal criteria which a doubtful haemal parasite might very well be required to satisfy in order to be considered as a Haemosporidian rather than a Haemoflagellate are (a) the occurrence of schizogony during the “corpuscular†phase in the Vertebrate host, and (b) the formation of many germs (“sporozoitesâ€) from the zygote; so long as these conditions were complied with, the present writer, at all events, would not feel he was countenancing any protozoological heresy in allowing for the possibility of a Flagellate (perhaps trypaniform) phase or features being present at some period or other in the life-cycle.1To render this article complete, however, one or two well-known parasites, hitherto referred to this order, must also be mentioned, which, judged by the above (arbitrary) standard, are, it may be, on the Haemoflagellate side of the dividing line (e.g.Halteridium, according to Schaudinn).
The chief characters which distinguish the Haemosporidia from other Ectospora are the following. They are invariably blood parasites, and for part or all of the trophic period come into intimate relation with the cellular elements in the blood. There is always an alternation of hosts and of generations, an Invertebrate being the definitive host, in which sexual conjugation is undergone and which is to be regarded as the primary one, a Vertebrate being the intermediate or secondary one. The zygote or sporont is at first capable of movement and known as an ookinete. No resistant spores (chlamydospores) are formed, the ultimate germs or sporozoites always being free in the oocyst and not enclosed by sporocysts.
To Sir E. Ray Lankester is due the honour of discovering the first Haemosporidian, a discovery which did not take place until after most of the other kinds of Sporozoa were known. In 1871 this author described the parasite of the frog, which he later termedDrepanidium ranarum. The next discovery was the great and far-reaching one of Laveran, who in 1883 described all the characteristic phases of the malarial parasite which are met with in human blood. While regarding the organism as the cause of the disease, Laveran did not at once recognize its animal and Sporozoan nature, but considered it rather as a vegetable, and termed itOscillaria malariae. As in the case of the Trypanosomes, we owe to Danilewsky (1885-1889) the first serious attempts to study the comparative anatomy and life-history of these parasites, from a zoological point of view. Danilewsky first named them Haemosporidia, and distinguished betweenHaemocytozoaandLeucocytozoa. To the brilliant researches of R. Ross and Grassi in the closing years of the 19th century is due the realization of the essential part played by the gnat or mosquito in the life-cycle and transmission of the parasites; and to MacCallum belongs the credit of first observing the true sexual conjugation, in the case of aHalteridium. Since then, thanks to the labours of Argutinsky and Schaudinn, our knowledge of the malarial parasites has steadily increased. Until quite recently, however, very little was known about the Haemosporidia of cold-blooded Vertebrates; but in 1903 Siegel and Schaudinn demonstrated that the same rôle is performed in their case by a leech or a tick, and since then many new forms have been described.
The Haemosporidia are widely distributed and of very general occurrence among the chief classes of Vertebrates. Among Invertebrates they are apparently limited to bloodsucking insects, ticks and leeches.2As already stated,Occurrence: habitat; effects on host.the universal habitat of the parasites in the Vertebrate is the blood; as a result, of course, they are to be met with in the capillaries of practically all the important organs of the body; and it is to be noted that while certain phases (e.g.growing trophozoites, mature gametocytes) are found in the peripheral circulation, others (e.g.schizogonous “rosettes,†young gametocytes) occur in the internal organs, liver, kidneys, &c., where the circulation is sluggish. The relation of the parasites to the blood-cells varies greatly. Most attack, probably exclusively, the red blood corpuscles (haematids); a few, however, select the leucocytes, and are therefore known as Leucocytozoa. In the case of Mammalian and Avian forms (malarial parasites) Schaudinn and Argutinsky have shown that the trophic and schizogonic phases are not really endoglobular but closely attached to the corpuscle, hollowing out a depression or space into which they nestle; the gametocytes, on the other hand, are actually intercellular. Forms parasitic in cold-blooded Vertebrates, on the contrary, are always, so far as is known, endoglobular when in relation with the corpuscles; and the same is apparently the case with the Mammalian parasite,Piroplasma. Although in no instance so far described is the parasite actually intranuclear (as certain Coccidia are), in one or two cases (e.g.Karyolysusof lizards and certain species ofHaemogregarina) it reacts markedly upon the nucleus and soon causes its disintegration. While many Haemosporidia (e.g.malarial parasites, with the exception ofHalteridium) remain in connexion with the same corpuscle throughout the whole period of growth and schizogony, the new generation of merozoites first being set free from the broken-down cell, others (the Haemogregarines,broadly speaking, and alsoHalteridium) leave one corpuscle after a short time, wander about free in the plasma, and then seek out another; and this may be repeated until the parasite is ready for schizogony, which generally occurs in the corpuscle.
As in the case of Trypanosomes (q.v.), normally—that is to say, when in an accustomed, tolerant host, and under natural conditions—Haemosporidia are non-pathogenic and do not give rise to any ill-effects in the animals harbouring them. When, however, the parasites gain an entry into the blood of man or other unadapted animals,3they produce, as is well known, harmful and often very serious effects. There are three recognized types of malarial fever, each caused by a distinct form and characterized by the mode of manifestation. Two, the so-called benign fevers, are intermittent; namely, tertian and quartan fever, in which the fever recurs every second and third day respectively. This is due to the fact that schizogony takes different lengths of time in the two cases, 48 hours in the one, 72 in the other; the height of the fever-period coincides with the break-down of the corpuscle at the completion of the process, and the liberation of great numbers of merozoites in the blood. The third type is the dangerous aestivo-autumnal or pernicious malaria, in which the fever is irregular or continuous during long periods.
A very general symptom is anaemia, which is sometimes present to a marked extent, when it may lead to a fatal termination. This is the result of the very considerable destruction of the blood-corpuscles which takes place, the haemoglobin of which is absorbed by the parasites as nutriment. A universal feature connected with this mode of nutrition is the production, in the cytoplasm of the parasite, of a brown pigment, termed melanin; this does not represent reserve material, but is an excretedby-product derived from the haemoglobin. These pigment-grains are at length liberated into the blood-stream and become deposited in the various organs, spleen, liver, kidneys, brain, causing pronounced pigmentation.
Another type of fever, more acute and more generally fatal, is that produced by forms belonging to the genusPiroplasma, in cattle, dogs, horses and other domestic animals in different regions of the globe; and recently Wilson and Chowning have stated that the “spotted fever of the Rockies†is a human piroplasmosis caused byP. hominis. The disease of cattle is known variously as Texas-fever, Tristeza, Red-water, Southern cattle-fever, &c. In this type of illness the endogenous multiplication of the parasites is very great and rapid, and brings about an enormous diminution in the number of healthy red blood corpuscles. Their sudden destruction results in the liberation of large quantities of haemoglobin in the plasma, which turns deep-red in colour; and hence haemoglobinuria, which occurs only rarely in malaria, is a constant symptom in piroplasmosis.
The parasite of pernicious malaria, here termedLaverania malariae, will serve very well as a type of the general life-cycle (fig. 1). Slight differences shown by the other malarial parasites (Plasmodium) will be mentioned in passing, but theExample of the life-history.main divergences which other Haemosporidian types exhibit are best considered separately. With the bite of an infected mosquito, the minute sickle-like sporozoites are injected into the blood. They rapidly penetrate into the blood corpuscles, in which they appear as small irregular, more or less amoeboid trophozoites. A vacuole next arises in the cytoplasm, which increases greatly in size, and gives rise to the well-known, much discussed ring-form of the parasite, in which it resembles a signet-ring, the nucleus forming a little thickening to one side. Some authorities (e.g.Argutinsky) have regarded this structure as being really a greatly distended vesicular nucleus, and, to a large extent, indeed, an artifact, resulting from imperfect fixation; but Schaudinn considers it is a true vacuole, and explains it on the ground of the rapid nutrition and growth. Later on this vacuole disappears, and the grains of pigment make their appearance. The trophozoite is now large and full-grown, and has become rounded and ready for schizogony. The nucleus of the schizont divides several times (more or less directly, by simple or multiple fission) to form a number of daughter-nuclei, which take up a regular position near the periphery. Around these the cytoplasm becomes segmented, giving rise to the well-knowncorps en rosace. Eventually the merozoites, in the form of little round uninuclear bodies, are liberated from the now broken-down corpuscle, leaving behind a certain amount of residual cytoplasm containing the pigment grains. Besides the difference in the time taken by the complete process of schizogony in the various species (see above), there are distinctions in the composition of the rosettes. Thus, inLaverania, the number of merozoites formed is very variable; inPlasmodium vivax(the tertian parasite) there are only few (9 to 12) merozoites, but inP. malariae(the quartan form) they are more numerous, from 12 to 24. The liberated merozoites proceed to infect fresh blood corpuscles and a new endogenous cycle is started.
After asexual multiplication has gone on for some time, sexual forms become developed. According to Schaudinn, the stimulus which determines the production of gametocytes instead of schizonts is the reaction of the host (at the height of a fever period) upon the parasites. A young trophozoite which is becoming a gametocyte is distinguished from one which gives rise to a schizont by its much slower rate of growth, and the absence of any vacuoles in its cytoplasm. The gametocytes themselves are characterized by their peculiar shape, like that of a sausage, whence they are very generally known as “crescents.†Male and female gametocytes are distinguished (roughly) by the arrangement of the pigment-grains; in the former, they are fairly evenly scattered throughout the cytoplasm, but in the megagametocytes the pigment tends to be aggregated centrally, around the nucleus. As they become full-grown and mature, however, the gametocytes lose their crescentic form and assume that of an oval, and finally of a sphere. At the same time, they are set free from the remains of the blood corpuscle. The spherical stage is practically the limit of development in the Vertebrate host, although, sometimes, the nucleus of the microgametocyte may proceed to division. The “crescents†of the pernicious parasite afford a very important diagnostic difference from the gametocytes of both species ofPlasmodium, which have the ordinary, rounded shape of the schizonts. In the case of the latter, points such as their slower growth, their less amoeboid character, and their size furnish the means of distinction.
When a gnat or mosquito sucks blood, all phases of the parasite in the peripheral circulation at that point may succeed in passing into the insect. If this occurs all trophic and schizogonic phases are forthwith digested, and the survival of the sexual phases depends entirely upon whether the insect is a gnat or mosquito. Only in the latter case can further development of the gametocytes go on; in other words, only the genusAnopheles, and not the genusCulex, furnishes specific hosts for the malarial parasites. This is a biological fact of considerable importance in connexion with the prophylactic measures against malaria. In the stomach of anAnopheles, the gametocytes quickly proceed to gamete-formation. The nucleus of the microgametocyte divides up, and the daughter-nuclei pass to the periphery. The surface of the body grows out into long, whip-like processes, of which there are usually 6 to 8 (probably the typical number is 8); each is very motile, in this respect strongly resembling a flagellum. This phase may also develop in drawn blood, which has, of course, become suddenly cooled by the exposure; and it seems evident that it is the change in temperature, from the warm to the cold-blooded host, which brings about the development of the actual sexual elements. Earlier observers regarded the phase just described as representing another parasite altogether, of a Flagellate nature—whence the well-known term,Polymitus-form; and even more recent workers, such as Labbé who connected it with the malarial parasite,failed to appreciate its true significance, and considered it rather as a degeneration-appearance. The micro-gametes soon liberate themselves from the residual cytoplasm of the parent and swim away in search of a megagamete; each is a very slender, wavy filament, composed largely of chromatic substance. The finer details of structure of the microgamete of a malarial parasite cannot be said, however, to be thoroughly known, and it is by no means impossible that its structure is really trypaniform, as, according to Schaudinn’s great work, is the case with the merozoites and sporozoites.
I.-V. and 6-10 show the schizogony.
VI.-XII., The sexual generation.
XIII., The motile zygote.
XIV.-XIX., Sporogony.
I.-III., Young amoebulae in blood-corpuscles.
IV., Older, actively amoeboid trophozoite.
V., Still older, less amoeboid trophozoite.
6, Mature schizont.
7, Schizont, with nucleus dividing up.
8, Young rosette stage.
9, Fully formed rosette stage.
10, Merozoites free in the blood by breaking down of the corpuscle.
VI., Young indifferent gametocyte.
VII.,a, Male crescent.
VII.,b, Female crescent.
VIII.,aandb, The gametocytes becoming oval.
IX.,aandb, Spherical gametocytes; in the male (IX.a) the nucleus has divided up.
X.,aandb, Formation of gametes; in the male (X.a) the so-called flagella or male gametes (fl) are thrown out, one of them is seen detached; in the female (X.b) a portion of the nucleus has been expelled.
XI., A male gamete penetrating a female gamete at a cone of reception formed near the nucleus.
XII., Zygote with two pronuclei in proximity.
XIII., Zygote in the motile stage (vermicule or oökinete).
XIV., Encysted zygote (oöcyst).
XV., Commencing multiplication of the nuclei in the oöcyst.
XVI., Oöcyst with numerous sporoblasts.
XVII., Commencing formation of sporozoites.
XVIII., Full-grown oocyst crammed with ripe sporozoites; on one side the cyst has burst and the sporozoites are escaping.
XIX., Free sporozoites, showing their changes of form.
n, Nucleus of the parasite.
p, Melanin pigment.
fl, “Flagella.â€
sp. bl., Sporoblasts.
r. n., Residual nuclei.
r. p., Residual protoplasm.
oes, Oesophagus.
st, Stomach.
cy, Cysts.
Mt, Malpighian tubules.
int, Intestine.
The megagametocyte becomes a megagamete directly after a process of maturation, which consists in the expulsion of a certain amount of nuclear substance. The actual conjugation is quite similar to the process in Coccidia, and the resulting zygote perfectly homologous. In the present case, however, the zygote does not at once secrete an oöcyst, with a thick resistant wall; on the contrary, it changes its shape, and becomes markedly gregariniform and active, and is known for this reason as an ookinete. The ookinete passes through the epithelial layer of the stomach, the thinner and more pointed end leading the way, and comes to rest in the connective tissue forming the outer layer of the stomach-wall (fig. 2). Here it becomes rounded and cyst-like, and grows considerably; for only a thin, delicate cyst-membrane is secreted, which does not impede the absorption of nutriment. Meanwhile, the nucleus has divided into several, around each of which the cytoplasm becomes segmented. Each of these segments (“blastophores,†“zoidophoresâ€) is entirely comparable to a sporoblast in the Coccidian oocyst, the chief difference being that it never forms a spore; moreover the segments or sporoblasts in the oocyst of a malarial parasite are irregular in shape and do not become completely separated from one another, but remain connected by thin cytoplasmic strands. Repeated multiplication of the sporoblast-nuclei next takes place, with the result that a great number of little nuclei are found all round the periphery. A corresponding number of fine cytoplasmic processes grow out from the surface, each carrying a nucleus with it, and in this manner ahuge number of slender, slightly sickle-shaped germs or sporozoites (“blasts,†“zoids,†&c.) are formed. Each oocyst may contain from hundreds to thousands of sporozoites.
When the sporogony (which lasts about 10 days) is completed, the oocyst ruptures and the sporozoites are set free into the body-cavity, leaving behind a large quantity of residual cytoplasm, including pigment grains, &c. The sporozoites are carried about by the blood-stream; ultimately, however, apparently by virtue of some chemotactic attraction, they practically all collect in the salivary glands, filling the secretory cells and also invading the ducts. When the mosquito next bites a man, numbers of them are injected, together with the minute drop of saliva, into his blood, where they begin a fresh endogenous cycle.
There is only one other point with regard to the life-history that need be mentioned. With the lapse of time all trophic and schizogonic (asexual) phases of the parasite in the blood die off. But it has long been known that malarial patients, apparently quite cured, may suddenly exhibit all the symptoms again, without having incurred a fresh infection. Schaudinn has investigated the cause of this recurrence, and finds that it is due to the power of the megagametocytes, which are very resistant and long-lived, to undergo a kind of parthenogenesis under favourable conditions and give rise to the ordinary asexual schizonts, which in turn can repopulate the host with all the other phases. Microgametocytes, on the other hand, die off in time if they cannot pass into a mosquito.
a, The form of the parasite found free in the blood-plasma.
b, Parasite within a blood-corpuscle, preparing for division; the nucleus has already divided.
c, The parasite has divided into two rounded corpuscles, which assume the form of the free parasite, as seen ind,eandf.
N, Nucleus of the blood-corpuscle.
n, Nucleus of the parasite. The outline of the blood-corpuscle is indicated by a thick black line.