FOOTNOTES:

Fig. 17. Ropy milk.Fig. 17. Ropy milk.

The communicable form of ropy milk only appears after the milk has been drawn from the udder for a day or so, and is caused by the development of various species of bacteria which find their way into the milk after it is drawn. These defects are liable to occur at any season of the year. Their presence in a dairy is a source of much trouble, as the unsightly appearance of the milk precludes its use as food, although there is no evidence that these ropy fermentations are dangerous to health.

There are undoubtedly a number of different species of bacteria that are capable of producing these viscid changes,[59]but it is quite probable that they are not of equal importance in infecting milk under natural conditions.

In the majority of cases studied in this country,[60]thecausal organism seems to beB. lactis viscosus, a form first found by Adametz in surface waters.[61]This organism possesses the property of developing at low temperatures (45°-50° F.), and consequently it is often able in winter to supplant the lactic-acid forms. Ward has found this germ repeatedly in water tanks where milk cans are cooled; and under these conditions it is easy to see how infection of the milk might occur. Marshall[62]reports an outbreak which he traced to an external infection of the udder; in another case, the slime-forming organism was abundant in the barn dust. A defect of this character is often perpetuated in a dairy for some time, and may therefore become exceedingly troublesome. In one instance in the writer's experience, a milk dealer lost over $150 a month for several months from ropy cream. Failure to properly sterilize cans, and particularly strainer cloths, is frequently responsible for a continuance of trouble of this sort.

The slimy substance formed in milk comes from various constituents of the milk, and the chemical character of the slime produced also varies with different germs. In some cases the slimy material is merely the swollen outer cell membrane of the bacteria themselves as in the case ofB. lactis viscosus; in others it is due to the decomposition of the proteids, but often the chief decomposition product appears to come from a viscous fermentation of the milk-sugar.

An interesting case of a fermentation of this class being utilized in dairying is seen in the use of "lange wei" (long or stringy whey) which is employed as a starter in Holland to control the gassy fermentations in Edam cheese.This slimy change is due to the growth ofStreptococcus Hollandicus.[63]

Alcoholic fermentations.Although glucose or cane-sugar solutions are extremely prone to undergo alcoholic fermentation, milk sugar does not readily undergo this change. Where such changes are produced it is due to yeasts. Several outbreaks attributable to such a cause have been reported.[64]Russell and Hastings[65]have found these milk-sugar splitting yeasts particularly abundant in regions where Swiss cheese is made, a condition made possible by the use of whey-soaked rennets in making such cheese.

Kephir and Koumiss are liquors much used in the Orient which are made from milk that has undergone alcoholic fermentation. Koumiss was originally made from mare's milk but is now often made from cows' milk by adding cane sugar and yeast. In addition to the CO2developed, alcohol, lactic acid, and casein-dissolving ferments are formed. Kephir is made by adding to milk Kephir grains, which are a mass of yeast and bacterial cells. The yeasts produce alcohol and CO2while the bacteria change the casein of milk, rendering it more digestible. These beverages are frequently recommended to persons who seem to be unable to digest raw milk readily. The exact nature of the changes produced are not yet well understood.[66]

Bitter milk.The presence of bitter substances in milk may be ascribed to a variety of causes. A number of plants, such as lupines, ragweed and chicory, possess the property of affecting milk when the same are consumed by animals.At certain stages in lactation, a bitter salty taste is occasionally to be noted that is peculiar to individual animals.

A considerable number of cases of bitter milk have, however, been traced to bacterial origin. For a number of years the bitter fermentation of milk was thought to be associated with the butyric fermentation, but Weigmann[67]showed that the two conditions were not dependent upon each other. He found that the organism which produced the bitter taste acted upon the casein.

Conn[68]observed a coccus form in bitter cream that was able to impart a bitter flavor to milk. Sometimes a bitter condition does not develop in the milk, but may appear later in the milk products, as in the case of a micrococcus which Freudenreich[69]found in cheese.

Harrison[70]has traced a common bitter condition in Canadian milk to a milk-sugar splitting yeast,Torula amarawhich not only grows rapidly in milk but produces an undesirable bitterness in cheddar cheese.

Cream ripened at low temperatures not infrequently develops a bitter flavor, showing that the optimum temperature for this type of fermentation is below the typical lactic acid change.

Milk that has been heated often develops a bitter condition. The explanation of this is that the bacteria producing the bitter substances usually possess endospores, and that while the boiling or sterilizing of milk easily kills the lactic acid germs, these forms on account of their greater resisting powers are not destroyed by the heat.

Soapy milk:A soapy flavor in milk was traced by Weigmann and Zirn[71]to a specific bacillus,B. lactis saponacei, that they found gained access to the milk in one case from the bedding and in another instance from hay. A similar outbreak has been reported in this country,[72]due to a germ acting on the casein and albumen.

Red milk.The most common trouble of this nature in milk is due to presence of blood, which is most frequently caused by some wound in the udder. The ingestion of certain plants as sedges and scouring rushes is also said to cause a bloody condition; madders impart a reddish tinge due to coloring matter absorbed. Defects of this class can be readily distinguished from those due to germ growth because they are apparent at time of milking. Where blood is actually present, the corpuscles settle out in a short time if left undisturbed.

There are a number of chromogenic or color-producing bacteria that are able to grow in milk, but their action is so slow that generally they are not of much consequence. Moreover their development is usually confined to the surface of the milk as it stands in a vessel. The most important is the well-knownB. prodigiosus. Another form found at times in milk possessing low acidity[73]isB. lactis erythrogenes. This species only develops the red color in the dark. In the light, it forms a yellow pigment. Various other organisms have been reported at different times.[74]

Blue milk.Blue milk has been known for many years, its communicable nature being established as long ago as 1838. It appears on the surface of milk first as isolatedparticles of bluish or grey color, which later become confluent, the blue color increasing in intensity as the acidity increases. The causal organism,B. cyanogenes, is very resistant toward drying,[75]thus accounting for its persistence. In Mecklenberg an outbreak of this sort once continued for several years. It has frequently been observed in Europe in the past, but is not now so often reported. Occasional outbreaks have been reported in this country.

Other kinds of colored milk.Two or three chromogenic forms producing still other colors have occasionally been found in milk. Adametz[76]discovered in a sample of cooked milk a peculiar form (Bacillus synxanthus) that produced a citron-yellow appearance which precipitated and finally rendered soluble the casein. Adametz, Conn, and List have described other species that confer tints of yellow on milk. Some of these are bright lemon, others orange, and some amber in color.

Still other color-producing bacteria, such as those that produce violet or green changes in the milk, have been observed. In fact, almost any of the chromogenic bacteria are able to produce their color changes in milk as it is such an excellent food medium. Under ordinary conditions, these do not gain access to milk in sufficient numbers so that they modify the appearance of it except in occasional instances.

Treatment of abnormal fermentations.If the taint is recognized as of bacterial origin (see p. 57) and is found in the mixed milk of the herd, it is necessary to ascertain, first, whether it is a general trouble, or restricted to one or more animals. This can sometimes be done by separatingthe milk of the different cows and noting whether any abnormal condition develops in the respective samples.

Fermentation tests.The most satisfactory way to detect the presence of the taints more often present is to make a fermentation test of one kind or another. These tests are most frequently used at the factory, to enable the maker to detect the presence of milk that is likely to prove unfit for use, especially in cheese making. They are based upon the principle that if milk is held at a moderately high temperature, the bacteria will develop rapidly. A number of different methods have been devised for this purpose. In Walther's lacto-fermentator samples of milk are simply allowed to stand in bottles or glass jars until they sour. They are examined at intervals of several hours. If the curdled milk is homogeneous and has a pure acid smell, the milk is regarded as all right. If it floats in a turbid serum, is full of gas or ragged holes, it is abnormal. As generally carried out, no attempt is made to have these vessels sterile. Gerber's test is a similar test that has been extensively employed in Switzerland. Sometimes a few drops of rennet are added to the milk so as to curdle the same, and thus permit of the more ready detection of the gas that is evolved.

Wisconsin curd test.The method of testing milk described below was devised at the Wisconsin Experiment Station in 1895 by Babcock, Russell and Decker.[77]It was used first in connection with experimental work on the influence of gas-generating bacteria in cheese making, but its applicability to the detection of all taints in milk produced by bacteria makes it a valuable test for abnormal fermentations in general.

In the curd test a small pat of curd is made in a glassjar from each sample of milk. These tests may be made in any receptacle that has been cleaned in boiling water, and to keep the temperature more nearly uniform these jars should be immersed in warm water, as in a wash tub or some other receptacle. When the milk is about 95° F., about ten drops of rennet extract are added to each sample and mixed thoroughly with the milk. The jars should then remain undisturbed until the milk is completely curdled; then the curd is cut into small pieces with a case knife and stirred to expel the whey. The whey should be poured off at frequent intervals until the curd mats. If the sample be kept at blood heat (98° F.) for six to eight hours, it will be ready to examine.

Fig. 18.Fig. 18.

Improved bottles for making curd test.A, test bottle complete;B, bottle showing construction of cover;S, sieve to hold back the curd when bottle is inverted;C, outer cover with(D H)drain holes to permit of removal of whey.]

More convenient types of this test than the improvised apparatus just alluded to have been devised by different dairy manufacturers. Generally, they consist of a special bottle having a full-sized top, thus permitting the easy removal of the curd. The one shown in Fig. 18 is providedwith a sieve of such construction that the bottles will drain thoroughly if inclined in an inverted position.

Interpretation of results of test.The curd from a good milk has a firm, solid texture, and should contain at most only a few small pin holes. It may have some large, irregular, "mechanical" holes where the curd particles have failed to cement, as is seen in Fig. 19. If gas-producing bacteria are very prevalent in the milk, the conditions under which the test is made cause such a rapid growth of the same that the evidence of the abnormal fermentation may be readily seen in the spongy texture of the curd (Fig. 20). If the undesirable organisms are not very abundant and the conditions not especially suited to their growth, the "pin holes" will be less frequent.

Fig. 19. Curd from a good milk. The large irregular holes are mechanical.Fig. 19. Curd from a good milk. The large irregular holes are mechanical.

Sometimes the curds show no evidence of gas, but their abnormal condition can be recognized by the "mushy" texture and the presence of "off" flavors that are rendered more apparent by keeping them in closed bottles. This condition is abnormal and is apt to produce quite as serious results as if gas was formed.

Overcoming taints by use of starters.Another method of combatting abnormal fermentations that is often fruitful, is that which rests upon the inability of one kind of bacteria to grow in the same medium in competition with certain other species.

Some of the undesirable taints in factories can be controlled in large part by the introduction of starters made from certain organisms that are able to obtain the ascendency over the taint-producing germ. Such a method is commonly followed when a lactic ferment, either a commercial pure culture, or a home-made starter, is added to milk to overcome the effect of gas-generating bacteria.

Fig. 20. Curd from a badly tainted milk. Large ragged holes are mechanical; numerous small holes due to gas. This curd was a "floater."Fig. 20. Curd from a badly tainted milk. Large ragged holes are mechanical; numerous small holes due to gas. This curd was a "floater."

A similar illustration is seen in the case of the "lange wei" (slimy whey), that is used in the manufacture of Edam cheese to control the character of the fermentation of the milk.

This same method is sometimes applied in dealing with certain abnormal fermentations that are apt to occur on the farm. It is particularly useful with those tainted milks known as "sweet curdling." The ferment organisms concernedin this change are unable to develop in the presence of lactic acid bacteria, so the addition of a clean sour milk as a starter restores the normal conditions by giving the ordinary milk bacteria the ascendency.

Chemical disinfection.In exceptional instances it may be necessary to employ chemical disinfectants to restore the normal conditions. Of course with such diseases as tuberculosis, very stringent measures are required, as they are such a direct menace to human life, but with these abnormal or taint-producing fermentations, care and cleanliness, well directed, will usually overcome the trouble.

If it becomes necessary to employ chemical substances as disinfecting agents, their use should always be preceded by a thorough cleansing with hot water so that the germicide may come in direct contact with the surface to be disinfected.

It must be borne in mind that many chemicals act as deodorants,i.e., destroy the offensive odor, without destroying the cause of the trouble.

Sulfuris often recommended as a disinfecting agent, but its use should be carefully controlled, otherwise the vapors have but little germicidal power. The common practice of burning a small quantity in a room or any closed space for a few moments has little or no effect upon germ life. The effect of sulfur vapor (SO2) alone upon germ life is relatively slight, but if this gas is produced in the presence of moisture, sulfurous acid (H2SO3) is formed, which is much more efficient. To use this agent effectively, it must be burned in large quantities in a moist atmosphere (three lbs. to every 1,000 cubic feet of space), for at least twelve hours. After this operation, the space should be thoroughly aired.

Formalin, a watery solution of a gas known as formaldehyde, is a new disinfectant that recent experience hasdemonstrated to be very useful. It may be used as a gas where rooms are to be disinfected, or applied as a liquid where desired. It is much more powerful in its action than sulfur, and it has a great advantage over mercury and other strong disinfectants, as it is not so poisonous to man as it is to the lower forms of life.

Bleaching powder or chloride of limeis often recommended where a chemical can be advantageously used. This substance is a good disinfectant as well as a deodorant, and if applied as a wash, in the proportion of four to six ounces of the powder to one gallon of water, it will destroy most forms of life. In many cases this agent is inapplicable on account of its odor.

Corrosive sublimate(HgCl2) for most purposes is a good disinfectant, but it is such an intense poison that its use is dangerous in places that are at all accessible to stock.

For the disinfection of walls in stables and barns, common thinwhite washCa(OH)2is admirably adapted if made from freshly-burned quick lime. It possesses strong germicidal powers, increases the amount of light in the barn, is a good absorbent of odors, and is exceedingly cheap.

Carbolic acid, creosote, and such products, while excellent disinfectants, cannot well be used on account of their odor, especially in factories.

For gutters, drains, and waste pipes in factories,vitriol salts(sulfates of copper, iron and zinc) are sometimes used. These are deodorants as well as disinfectants, and are not so objectionable to use on account of their odor.

These suggestions as to the use of chemicals, however, only apply to extreme cases and should not be brought into requisition until a thorough application of hot water, soap, a little soda, and the scrubbing brush have failed to do their work.

FOOTNOTES:[51]Günther and Thierfelder, Arch. f. Hyg., 25:164, 1895; Leichmann, Cent. f. Bakt., 2:281, 1896; Esten, 9 Rept. Storrs Expt. Stat., p. 44, 1896; Dinwiddie, Bull. 45, Ark. Expt. Stat., May, 1897; Kozai, Zeit. f. Hyg., 38:386, 1901; Weigmann, Hyg. Milk Congress, Hamburg, 1903, p. 375.[52]McDonnell, Inaug. Diss., Kiel. 1899, p. 39.[53]Kayser, Cent. f. Bakt. II. Abt. 1:436.[54]Treadwell, Science, 1894, 17:178.[55]Conn, 5 Rept. Storrs Expt. Stat., 1892, p. 396.[56]Fermi, Arch. f. Hyg., 1892, 14:1.[57]Duclaux, Le Lait, p. 121.[58]Duclaux, Principes de Laiterie, p. 67.[59]Guillebeau (Milch Zeit., 1892, p. 808) has studied over a dozen different forms that possess this property.[60]Ward, Bull. 165, Cornell Expt. Stat., Mch., 1899; also Bull. 195, Ibid., Nov., 1901.[61]Adametz, Landw. Jahr., 1891, p. 185.[62]Marshall, Mich. Expt. Stat., Bull. 140.[63]Milch Zeit., 1899, p. 982.[64]Duclaux, Principes de Laiterie, p. 60. Heinze and Cohn, Zeit. f. Hyg., 46: 286, 1904.[65]Bull. 128, Wis. Expt. Stat., Sept. 1905.[66]Freudenreich, Landw. Jahr. d. Schweiz, 1896, 10; 1.[67]Weigmann, Milch Zeit., 1890, p. 881.[68]Conn, 3 Rept. Storrs Expt. Stat., 1890, p. 158.[69]Freudenreich, Fühl. Landw. Ztg. 43: 361.[70]Harrison, Bull. 120 Ont. Agr'l. Coll., May, 1902.[71]Milch Zeit. 22:569.[72]Marshall, Bull. 146, Mich. Expt. Stat., p. 16.[73]Grotenfelt, Milch Zeit., 1889, p. 263.[74]Menge, Cent. f. Bakt., 6:596; Keferstein, Cent. f. Bakt., 21:177.[75]Heim, Arb. a. d. Kais. Gesundheitsamte, 5:578.[76]Adametz, Milch Zeit., 1890, p. 225.[77]12 Rept. Wis. Expt. Stat., 1895, p. 148; also Bull. 67, Ibid., June, 1898.

[51]Günther and Thierfelder, Arch. f. Hyg., 25:164, 1895; Leichmann, Cent. f. Bakt., 2:281, 1896; Esten, 9 Rept. Storrs Expt. Stat., p. 44, 1896; Dinwiddie, Bull. 45, Ark. Expt. Stat., May, 1897; Kozai, Zeit. f. Hyg., 38:386, 1901; Weigmann, Hyg. Milk Congress, Hamburg, 1903, p. 375.

[52]McDonnell, Inaug. Diss., Kiel. 1899, p. 39.

[53]Kayser, Cent. f. Bakt. II. Abt. 1:436.

[54]Treadwell, Science, 1894, 17:178.

[55]Conn, 5 Rept. Storrs Expt. Stat., 1892, p. 396.

[56]Fermi, Arch. f. Hyg., 1892, 14:1.

[57]Duclaux, Le Lait, p. 121.

[58]Duclaux, Principes de Laiterie, p. 67.

[59]Guillebeau (Milch Zeit., 1892, p. 808) has studied over a dozen different forms that possess this property.

[60]Ward, Bull. 165, Cornell Expt. Stat., Mch., 1899; also Bull. 195, Ibid., Nov., 1901.

[61]Adametz, Landw. Jahr., 1891, p. 185.

[62]Marshall, Mich. Expt. Stat., Bull. 140.

[63]Milch Zeit., 1899, p. 982.

[64]Duclaux, Principes de Laiterie, p. 60. Heinze and Cohn, Zeit. f. Hyg., 46: 286, 1904.

[65]Bull. 128, Wis. Expt. Stat., Sept. 1905.

[66]Freudenreich, Landw. Jahr. d. Schweiz, 1896, 10; 1.

[67]Weigmann, Milch Zeit., 1890, p. 881.

[68]Conn, 3 Rept. Storrs Expt. Stat., 1890, p. 158.

[69]Freudenreich, Fühl. Landw. Ztg. 43: 361.

[70]Harrison, Bull. 120 Ont. Agr'l. Coll., May, 1902.

[71]Milch Zeit. 22:569.

[72]Marshall, Bull. 146, Mich. Expt. Stat., p. 16.

[73]Grotenfelt, Milch Zeit., 1889, p. 263.

[74]Menge, Cent. f. Bakt., 6:596; Keferstein, Cent. f. Bakt., 21:177.

[75]Heim, Arb. a. d. Kais. Gesundheitsamte, 5:578.

[76]Adametz, Milch Zeit., 1890, p. 225.

[77]12 Rept. Wis. Expt. Stat., 1895, p. 148; also Bull. 67, Ibid., June, 1898.

Practical experience with epidemic disease has abundantly demonstrated the fact that milk not infrequently serves as a vehicle for the dissemination of contagion. Attention has been prominently called to this relation by Ernest Hart,[78]who in 1880 compiled statistical evidence showing the numerous outbreaks of various contagious diseases that had been associated with milk infection up to that time. Since then, further compilations have been made by Freeman,[79]and also by Busey and Kober,[80]who have collected the data with reference to outbreaks from 1880 to 1899.

These statistics indicate the relative importance of milk as a factor in the dissemination of disease.

The danger from this source is much intensified for the reason that milk, generally speaking, is consumed in a raw state; and also because a considerable number of disease-producing bacteria are able, not merely to exist, but actually thrive and grow in milk, even though the normal milk bacteria are also present. Moreover the recognition of the presence of such pathogenic forms is complicated by the fact that often they do not alter the appearance ofthe milk sufficiently so that their presence can be detected by a physical examination. These facts which have been experimentally determined, coupled with the numerous clinical cases on record, make a strong case against milk serving as an agent in the dissemination of disease.

Origin of pathogenic bacteria in milk.Disease-producing bacteria may be grouped with reference to their relation toward milk into two classes, depending upon the manner in which infection occurs:

Class I. Disease-producing bacteria capable of being transmitted directly from a diseased animal to man through the medium of infected milk.

Class II. Bacteria pathogenic for man but not for cattle which are capable of thriving in milk after it is drawn from the animal.

In the first group the disease produced by the specific organism must be common to both cattle and man. The organism must live a parasitic life in the animal, developing in the udder, and so infect the milk supply. It may, of course, happen that diseases toward which domestic animals alone are susceptible may be spread from one animal to another in this way without affecting human beings.

In the second group, the bacterial species lives a saprophytic existence, growing in milk, if it happens to find its way therein. In such cases milk indirectly serves as an agent in the dissemination of disease, by giving conditions favorable to the growth of the disease germ.

By far the most important of diseases that may be transmitted directly from animal to man through a diseased milk supply is tuberculosis, but in addition to this, foot and mouth disease (aphthous fever in children), anthrax and acute enteric troubles have also been traced to a similar source of infection.

The most important specific diseases that have been disseminated through subsequent pollution of the milk are typhoid fever, diphtheria, scarlet fever and cholera, but, of course, the possibility exists that any disease germ capable of living and thriving in milk may be spread in this way. In addition to these diseases that are caused by the introduction of specific organisms (the causal organism of scarlet fever has not yet been definitely determined), there are a large number of more or less illy-defined troubles of an intestinal character that occur especially in infants and young children that are undoubtedly attributable to the activity of microörganisms that gain access to milk during and subsequent to the milking, and which produce changes in milk before or after its ingestion that result in the formation of toxic products.

Tuberculosis.In view of the wide-spread distribution of this disease in both the human and the bovine race, the relation of the same to milk supplies is a question of great importance. It is now generally admitted that the different types of tubercular disease found in different kinds of animals and man are attributable to the development of the same organism,Bacillus tuberculosis, although there are varieties of this organism found in different species of animals that are sufficiently distinct to permit of recognition.

The question of prime importance is, whether the bovine type is transmissible to the human or not. Artificial inoculation of cattle with tuberculous human sputum as well as pure cultures of this variety show that the human typeis able to make but slight headway in cattle. This would indicate that the danger of cattle acquiring the infection from man would in all probability be very slight, but these experiments offer no answer as to the possibility of transmission from the bovine to the human. Manifestly it is impossible to solve this problem by direct experiment upon man except by artificial inoculation, but comparative experiments upon animals throw some light on the question.

Theo. Smith[81]and others[82]have made parallel experiments with animals such as guinea pigs, rabbits and pigeons, inoculated with both bovine and human cultures of this organism. The results obtained in the case of all animals tested show that the virulence of the two types was much different, but that the bovine cultures were much more severe. While of course this does not prove that transmission from bovine to human is possible, still the importance of the fact must not be overlooked.

In a number of cases record of accidental infection from cattle to man has been noted.[83]These have occurred with persons engaged in making post-mortem examinations on tuberculous animals, and the tubercular nature of the wound was proven in some cases by excision and inoculation.

In addition to data of this sort that is practically experimental in character, there are also strong clinical reasons for considering that infection of human beings may occur through the medium of milk. Naturally such infection should produce intestinal tuberculosis, and it is noteworthy that this phase of the disease is quite common in childrenespecially between the ages of two and five.[84]It is difficult to determine, though, whether primary infection occurred through the intestine, for, usually, other organs also become involved. In a considerable number of cases in which tubercular infection by the most common channel, inhalation, seems to be excluded, the evidence is strong that the disease was contracted through the medium of the milk, but it is always very difficult to exclude the possibility of pulmonary infection.

Tuberculosis as a bovine disease has increased rapidly during recent decades throughout many portions of the world. This has been most marked in dairy regions. Its extremely insidious nature does not permit of an early recognition by physical means, and it was not until the introduction of the tuberculin test[85]in 1892, as a diagnostic aid that accurate knowledge of its distribution was possible. The quite general introduction of this test in many regions has revealed an alarmingly large percentage of animals as affected. In Denmark in 1894 over forty per cent were diagnosed as tubercular. In some parts of Germany almost as bad a condition has been revealed. Slaughter-house statistics also show that the disease has increased rapidly since 1890. In this country the disease on the average is much less than in Europe and is also very irregularly distributed. In herds where it gained a foothold some years ago, often the majority of animals are frequently infected; manyherds, in fact the great majority, are wholly free from all taint. The disease has undoubtedly been most frequently introduced through the purchase of apparently healthy but incipiently affected animals. Consequently in the older dairy regions where stock has been improved the most by breeding, more of the disease exists than among the western and southern cattle.

Fig. 21: Front view of a tuberculous udder, showing extent of swelling in single quarter.Fig. 21: Front view of a tuberculous udder, showing extent of swelling in single quarter.

Infectiousness of milk of reacting animals.Where the disease appears in the udder the milk almost invariably contains the tubercle organism. Under such conditions the appearance of the milk is not materially altered at first, but as the disease progresses the percentage of fat generally diminishes, and at times in the more advanced stages where the physical condition of the udder is changed (Fig. 21),the milk may become "watery"; but the percentage of animals showing such udder lesions is not large, usually not more than a few per cent. (4 per cent. according to Ostertag.)

On the other hand, in the earlier phases of the disease, where its presence has been recognized solely by the aid of the tuberculin test, before there are any recognizable physical symptoms in any part of the animal, the milk is generally unaffected. Between these extremes, however, is found a large proportion of cases, concerning which so definite data are not available. The results of investigators on this point are conflicting and further information is much desired. Some have asserted so long as the udder itself shows no lesions that no tubercle bacilli would be present,[86]but the findings of a considerable number of investigators[87]indicate that even when the udder is apparently not diseased the milk may contain the specific organism as revealed by inoculation experiments upon animals. In some cases, however, it has been demonstrated by post-mortem examination that discoverable udder lesions existed that were not recognizable before autopsy was made. In the experimental evidence collected, a varying percentage of reacting animals were found that gave positive results; and this number was generally sufficient to indicate that the danger of using milk from reacting animals was considerable, even though apparently no disease could be found in the udder.

The infectiousness of milk can also be proven by the frequent contraction of the disease in other animals, such as calves and pigs which may be fed on the skim milk. The very rapid increase of the disease among the swine of Germanyand Denmark,[88]and the frequently reported cases of intestinal infection of young stock also attest the presence of the organism in milk.

The tubercle bacillus is so markedly parasitic in its habits, that, under ordinary conditions, it is incapable of growing at normal air temperatures. There is, therefore, no danger of the germ developing in milk after it is drawn from the animal, unless the same is kept at practically blood heat.

Even though the milk of some reacting animals may not contain the dangerous organism at the time of making the test, it is quite impossible to foretell how long it will remain free. As the disease becomes more generalized, or if tuberculous lesions should develop in the udder, the milk may pass from a healthy to an infectious state.

This fact makes it advisable to exclude from milk supplies intended for human use, all milk of animals that respond to the tuberculin test; or at least to treat it in a manner so as to render it safe. Whether it is necessary to do this or not if the milk is made into butter or cheese is a somewhat different question. Exclusion or treatment is rendered more imperative in milk supplies, because the danger is greater with children with whom milk is often a prominent constituent of their diet, and also for the reason that the child is more susceptible to intestinal infection than the adult.

The danger of infection is much lessened in butter or cheese, because the processes of manufacture tend to diminish the number of organisms originally present in the milk, and inasmuch as no growth can ordinarily take place in these products the danger is minimized. Moreover, the fact thatthese foods are consumed by the individual in smaller amounts than is generally the case where milk is used, and also to a greater extent by adults, lessens still further the danger of infection.

Notwithstanding this, numerous observers[89]especially in Germany have succeeded in finding the tubercle bacillus in market butter, but this fact is not so surprising when it is remembered that a very large fraction of their cattle show the presence of the disease as indicated by the tuberculin test, a condition that does not obtain in any large section in this country.

The observations on the presence of the tubercle bacillus in butter have been questioned somewhat of late[2] by the determination of the fact that butter may contain an organism that possesses the property of being stained in the same way as the tubercle organism. Differentiation between the two forms is rendered more difficult by the fact that this tubercle-like organism is also capable of producing in animals lesions that stimulate those of tuberculosis, although a careful examination reveals definite differences. Petri[90]has recently determined that both the true tubercle and the acid-resisting butter organism may be readily found in market butter.

In the various milk products it has been experimentally determined that the true tubercle bacillus is able to retain its vitality in butter for a number of months and in cheese for nearly a year.

Treatment of milk from tuberculosis cows.While it has been shown that it is practically impossible to foretell whether the milk of any reacting animal actually containstubercle bacilli or not, still the interests of public health demand that no milk from such stock be used for human food until it has been rendered safe by some satisfactory treatment.

1. Heating.By far the best treatment that can be given such milk is to heat it. The temperature at which this should be done depends upon the thermal death point of the tubercle bacillus, a question concerning which there has been considerable difference of opinion until very recently. According to the work of some of the earlier investigators, the tubercle bacillus in its vegetative stage is endowed with powers of resistance greater than those possessed by any other pathogenic organism. This work has not been substantiated by the most recent investigations on this subject. In determining the thermal death point of this organism, as of any other, not only must the temperature be considered, but the period of exposure as well, and where that exposure is made in milk, another factor must be considered, viz., the presence of conditions permitting of the formation of a "scalded layer," for as Smith[91]first pointed out, the resistance of the tubercle organism toward heat is greatly increased under these conditions. If tuberculous milk is heated in a closed receptacle where this scalded membrane cannot be produced, the tubercle bacillus is killed at 140° F. in 15 to 20 minutes. These results which were first determined by Smith, under laboratory conditions, and confirmed by Russell and Hastings,[92]where tuberculous milk was heated in commercial pasteurizers, have also been verified by Hesse.[93]A great practical advantage which accrues from the treatment of milk at140° F. is that the natural creaming is practically unaffected. Of course, where a higher temperature is employed, the period of exposure may be materially lessened. If milk is momentarily heated to 176° F., it is certainly sufficient to destroy the tubercle bacillus. This is the plan practiced in Denmark where all skim milk and whey must be heated to this temperature before it can be taken back to the farm, a plan which is designed to prevent the dissemination of tuberculosis and foot and mouth disease by means of the mixed creamery by-products. This course renders it possible to utilize with perfect safety, for milk supplies, the milk of herds reacting to the tuberculin test, and as butter of the best quality can be made from cream or milk heated to even high temperatures,[94]it thus becomes possible to prevent with slight expense what would otherwise entail a large loss.

2. Dilution.Another method that has been suggested for the treatment of this suspected milk is dilution with a relatively large volume of perfectly healthy milk. It is a well known fact that to produce infection, it requires the simultaneous introduction of a number of organisms, and in the case of tuberculosis, especially that produced by ingestion, this number is thought to be considerable. Gebhardt[95]found that the milk of tuberculous cows, which was virulent when injected by itself into animals, was innocuous when diluted with 40 to 100 times its volume of healthy milk. This fact is hardly to be relied upon in practice, unless the proportion of reacting to healthy cows is positively known.

It has also been claimed in the centrifugal separation ofcream from milk[96]that by far the larger number of tubercle bacilli were thrown out with the separator slime. Moore[97]has shown that the tubercle bacilli in an artificially infected milk might be reduced in this way, so as to be no longer microscopically demonstrable, yet the purification was not complete enough to prevent the infection of animals inoculated with the milk.

Another way to exclude all possibility of tubercular infection in milk supplies is to reject all milk from reacting animals. This method is often followed where pasteurization or sterilization is not desired. In dairies where the keeping quality is dependent upon the exclusion of bacteria by stringent conditions as to milking and handling ("sanitary" or "hygienic" milk), the tuberculin test is frequently used as a basis to insure healthy milk.

Foot and mouth disease.The wide-spread extension of this disease throughout Europe in recent years has given abundant opportunity to show that while it is distinctively an animal malady, it is also transmissible to man, although the disease is rarely fatal. The causal organism has not been determined with certainty, but it has been shown that the milk of affected animals possesses infectious properties[98]although appearing unchanged in earlier phases of the disease.

Hertwig showed the direct transmissibility of the disease to man by experiments made on himself and others. By ingesting milk from an affected animal, he was able to produce the symptoms of the disease, the mucous membrane of the mouth being covered with the small vesicles that characterize the malady. It has also been shown thatthe virus of the disease may be conveyed in butter.[99]This disease is practically unknown in this country, although widely spread in Europe.

There are a number of other bovine diseases such as anthrax,[100]lockjaw,[101]and hydrophobia[102]in which it has been shown that the virus of the disease is at times to be found in the milk supply, but often the milk becomes visibly affected, so that the danger of using the same is greatly minimized.

There are also a number of inflammatory udder troubles known as garget or mammitis. In most of these, the physical appearance of the milk is so changed, and often pus is present to such a degree as to give a very disagreeable appearance to the milk. Pus-forming bacteria (staphylococci and streptococci) are to be found associated with such troubles. A number of cases of gastric and intestinal catarrh have been reported as caused by such milks.[103]

Milk is so well adapted to the development of bacteria in general, that it is not surprising to find it a suitable medium for the growth of many pathogenic species even at ordinary temperatures. Not infrequently, disease-producing bacteria are able to grow in raw milk in competition with the normal milk bacteria, so that even a slight contamination may suffice to produce infection.

The diseases that are most frequently disseminated inthis way are typhoid fever, diphtheria, scarlet fever and cholera, together with the various illy-defined intestinal troubles of a toxic character that occur in children, especially under the name of cholera infantum, summer complaint, etc.

Diseases of this class are not derived directly from animals because cattle are not susceptible to the same.

Modes of infection.In a variety of ways, however, the milk may be subject to contaminating influences after it is drawn from the animal, and so give opportunity for the development of disease-producing bacteria. The more important methods of infection are as follows:

1. Infection directly from a pre-existing case of disease on premises.Quite frequently a person in the early stage of a diseased condition may continue at his usual vocation as helper in the barn or dairy, and so give opportunity for direct infection to occur. In the so-called cases of "walking typhoid," this danger is emphasized. It is noteworthy in typhoid fever that the bacilli frequently persist in the urine and in diphtheria they often remain in the throat until after convalescence. In some cases infection has been traced to storage of the milk in rooms in the house where it became polluted directly by the emanations of the patient.[104]Among the dwellings of the lower classes where a single room has to be used in common this source of infection has been most frequently observed.

2. Infection through the medium of another person.Not infrequently another individual may serve in the capacity of nurse or attendant to a sick person, and also assist in the handling of the milk, either in milking the animals orcaring for the milk after it has been drawn. Busey and Kober report twenty-one outbreaks of typhoid fever in which dairy employees also acted in the capacity of nurses.

3. Pollution of milk utensils.The most frequent method of infection of cans, pails, etc., is in cleaning them with water that may be polluted with disease organisms. Often wells may be contaminated with diseased matter of intestinal origin, as in typhoid fever, and the use of water at normal temperatures, or even in a lukewarm condition, give conditions permitting of infection. Intentional adulteration of milk with water inadvertently taken from polluted sources has caused quite a number of typhoid outbreaks.[105]Sedgwick and Chapin[106]found in the Springfield, Mass., epidemic of typhoid that the milk cans were placed in a well to cool the milk, and it was subsequently shown that the well was polluted with typhoid fecal matter.

4. Pollution of udderof animalby wading in infected water, or by washing same with contaminated water. This method of infection would only be likely to occur in case of typhoid. An outbreak at the University of Virginia in 1893[107]was ascribed to the latter cause.

5. Pollution of creamery by-products, skim-milk, etc.Where the milk supply of one patron becomes infected with pathogenic bacteria, it is possible that disease may be disseminated through the medium of the creamery, the infective agent remaining in the skim milk after separation and so polluting the mixed supply. This condition is more likely to prevail with typhoid because of the greater tolerance of this organism for acids such as would be found in rawmilk. The outbreaks at Brandon,[108]England, in 1893, Castle Island,[109]Ireland, and Marlboro,[110]Mass., in 1894, were traced to such an origin.

While most outbreaks of disease associated with a polluted milk supply originate in the use of the milk itself, yet infected milk may serve to cause disease even when used in other ways. Several outbreaks of typhoid fever have been traced to the use of ice cream where there were strong reasons for believing that the milk used in the manufacture of the product was polluted.[111]Hankin[112]details a case of an Indian confection made largely from milk that caused a typhoid outbreak in a British regiment.

Although the evidence that milk may not infrequently serve as an agent in spreading disease is conclusive enough to satisfactorily prove the proposition, yet it should be borne in mind that the organism of any specific disease in question has rarely ever been found. The reasons for this are quite the same as those that govern the situation in the case of polluted waters, except that the difficulties of the problem are much greater in the case of milk than with water. The inability to readily separate the typhoid germ, for instance, from the colon bacillus, an organism frequently found in milk, presents technical difficulties not easily overcome. The most potent reason of failure to find disease bacteria is the fact that infection in any case must occur sometime previous to the appearance of the outbreak. Not only is there the usual period of incubation, but it rarely happens that an outbreak is investigated until a number ofcases have occurred. In this interim the original cause of infection may have ceased to be operative.

Typhoid fever.With reference to the diseases likely to to be disseminated through the medium of milk, infected after being drawn from the animal, typhoid fever is the most important. The reason for this is due (1) to the wide spread distribution of the disease; (2) to the fact that the typhoid bacillus is one that is capable of withstanding considerable amounts of acid, and consequently finds even in raw milk containing the normal lactic acid bacteria conditions favorable for its growth.[113]Ability to grow under these conditions can be shown not only experimentally, but there is abundant clinical evidence that even a slight infection often causes extensive outbreaks, as in the Stamford, Conn., outbreak in 1895 where 386 cases developed in a few weeks, 97 per cent. of which occurred on the route of one milk-man. In this case the milk cans were thoroughly and properly cleaned, but were rinsed out withcoldwater from a shallow well that was found to be polluted.

The most common mode of pollution of milk with typhoid organisms is where the milk utensils are infected in one way or another.[114]Second in importance is the carrying of infection by persons serving in the dual capacity of nurse and dairy attendant.

Cholera.This germ does not find milk so favorable a nutrient medium as the typhoid organism, because it is much more sensitive toward the action of acids. Kitasato[115]found, however, that it could live in raw milk from one to four days, depending upon the amount of acid present. In boiled or sterilized milk it grows more freely, as the acid-producing forms are thereby eliminated. In butter it dies out in a few days (4 to 5).

On account of the above relation not a large number of cholera outbreaks have been traced to milk, but Simpson[116]records a very striking case in India where a number of sailors, upon reaching port, secured a quantity of milk. Of the crew which consumed this, every one was taken ill, and four out of ten died, while those who did not partake escaped without any disease. It was later shown that the milk was adulterated with water taken from an open pool in a cholera infected district.

Diphtheria.Milk occasionally, though not often, serves as a medium for the dissemination of diphtheria. Swithinbank and Newman[117]cites four cases in which the causal organism has been isolated from milk. It has been observed that growth occurs more rapidly in raw than in sterilized milk.[118]

Infection in this disease is more frequently attributable to direct infection from patient on account of the long persistence of this germ in the throat, or indirectly through the medium of an attendant.

Scarlet fever.Although it is more difficult to study the relation of this disease to contaminated milk supplies, because the causal germ of scarlet fever is not yet known, yet the origin of a considerable number of epidemics hasbeen traced to polluted milk supplies. Milk doubtless is infected most frequently from persons in the earlier stages of the disease when the infectivity of the disease is greater.

Diarrhoeal diseases.Milk not infrequently acquires the property of producing diseases of the digestive tract by reason of the development of various bacteria that form more or less poisonous by-products. These troubles occur most frequently during the summer months, especially with infants and children, as in cholera infantum and summer complaint. The higher mortality of bottle-fed infants[119]in comparison with those that are nursed directly is explicable on the theory that cows' milk is the carrier of the infection, because in many cases it is not consumed until there has been ample time for the development of organisms in it. Where milk is pasteurized or boiled it is found that the mortality among children is greatly reduced. As a cause of sickness and death these diseases exceed in importance all other specific diseases previously referred to. These troubles have generally been explained as produced by bacteria of the putrefactive class which find their way into the milk through the introduction of filth and dirt at time of milking.[120]Flügge[121]has demonstrated that certain peptonizing species possess toxic properties for animals. Recent experimental inquiry[122]has demonstrated that the dysentery bacillus (Shiga) probably bears a causal relation to some of these summer complaints.

Ptomaine poisoning.Many cases of poisoning from food products are also reported with adults. These are due to the formation of various toxic products, generally ptomaines, that are produced as a result of infection of foods by different bacteria. One of these substances,tyrotoxicon, was isolated by Vaughan[123]from cheese and various other products of milk, and found to possess the property of producing symptoms of poisoning similar to those that are noted in such cases. He attributes the production of this toxic effect to the decomposition of the elements in the milk induced by putrefactive forms of bacteria that develop where milk is improperly kept.[124]Often outbreaks of this character[125]assume the proportions of an epidemic, where a large number of persons use the tainted food.

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