[5]. Annales de l’Institut Pasteur, September, 1898.
This may explain the reported cases in which a flock of poultry have developed tuberculosis a few months after they were placed in the hands of a consumptive caretaker. That such transmission does not always occur is not surprising, considering that transmission between man and man is infrequent in comparison with the number of exposures. So in cattle the majority of exposed animals usually escape, although in such a case there can be no plausible explanation on the ground of a difference of germ. We have in every case to consider the necessity for receptivity as well as infectivity, and the lack of either is a bar to infection. When, however, we assume that the most diverse tubercle bacilli are descendent’s of one original stock, that a large herd must furnish some animals of more than usual susceptibility, and that such animals are subjected to continuous accessions of both bacilli and toxins, we can easily understand how some of the more adaptable germs will in time accommodate themselves to the new medium. A Pettinkoffer, with an immune constitution or a specially vigorous gastric digestion, may with impunity drink a culture of cholera spirillum, but the same is not true of the drunkard fresh from a spree and with seriously impaired digestion.
Bacillus Tuberculosis in Man and Ox. Points of Similarity. The bacillus tuberculosis of cattle is in general shorter and thicker than those of man, but many in both subjects are morphologically indistinguishable. Such differences are often far exceeded by different specimens of one stock of germ seeded on different media. There is no great difference in the thermal death point, and the viability in light, dryness, cold and putrefaction. The tendency is in all cases to colonize the lymph plexus or glands and to develop the specific lesions, with slight variation in detail. The slow development of the lesions from both forms of bacilli and their histological similarity is another argument for their essential identity. The slow growth of both on artificial media, the demand of each for a medium having the same approximate composition, and the similar pathogenic and diagnostic characters of the toxic matters elaborated by both germs bespeak a primary identity. The very remarkable staining qualities of tubercle bacillus, from whatever source it may be drawn, are no less remarkable.
Tuberculosis of Man and Ox Coextensive. The prevalence of tuberculosis in man and ox in the same country and district is so frequent that it may be safely set down as the rule. Among ichthyophagists and great fishing communities, like the people of the Hebrides, Iceland, Newfoundland, Greenland, and the coasts of Hudson Bay, tuberculosis is rare. In these countries cattle are few or absent, or, like the hardy highland kyloes of the Hebrides, they are kept in the open air. The immunity of the people is not due to insusceptibility, since they fall ready victims to tuberculosis when removed to infected countries and cities.
In Northern Sweden, Norway, Lapland and Finland, where cattle are scarce and reindeer plentiful, tuberculosis is said to be rare, though the inhabitants live in the closest of dwellings through the long winter. In most of the Pacific islands there are no cattle, and the natives are comparatively free from consumption. In Hawaii, since the introduction of cattle, consumption has increased. Australia and Tasmania, which forty years ago were the great resorts for English consumptives, have become increasingly the homes of infection since the development of the cattle industry and the influx of phthisical subjects. Minnesota and Dakota, in the early days, were held to be incompatible with tuberculosis, but since the advent of the white man and his stabled herds they have largely lost their sanitary reputation. The highest known mortality from tuberculosis to-day is that of the reservation Indians of these States, who feed on raw, diseased beef. In the Kighiz steppes the Tartars subsist on the flesh and milk of their solipeds, and largely escape consumption. In Japan, Dr. Ashmead tells us that the common people escape tuberculosis, while the aristocracy suffer severely. He attributes this mainly to the debauchery of the ruling class; but it must not be overlooked that they eat freely of beef and dairy products, which the rice-eating poorer population do not. The same remarks apply in measure to the mandarin and plebian classes in China. Holden tells us that tuberculosis is rare in Columbia, Ecuador and on the eastern slopes of the Andes, where little or no milk or butter is used. It must be further borne in mind that in these countries all herds live in the open air, and practically escape infection.
These examples must be contrasted with the consumers of beef and milk in civilized temperate countries, where the stock are largely kept indoors. A general average mortality of 7 or 8 per cent. from tuberculosis, and the post mortem evidence in European and American hospitals of 33 to 50 per cent. which show tubercular lesions, recent or remote, cannot be lightly passed over. The contrast with our reservation Indians is still more striking. Holden and Treon testify that the meat furnished to the Indians is always poor and often diseased, and that when the stock arrives our hungry wards devour the internal organs raw, or, later, the flesh as pounded preserved meat, and still uncooked. The deaths of these Indians from tuberculosis is 50 per cent. of the total mortality.[[6]] Dr. Washington Matthews, who spent twenty-one years among the Indians, gives their food as the main cause of the disease, and states that when the supply of fresh meat is liberal the death rate from tuberculosis is highest (Census of 1880).
[6]. Medical Record, August 13, 1883.
If we now contrast this fearful mortality with the immunity of the Indians of Hudson Bay, Great Slave Lake, Alaska, and the North generally, we have a most suggestive picture. It may be conceded that the extreme Northern Indians, being beyond the cereal region, have a slight measure of protection in their meat diet; but the recent spread of tuberculosis, like a plague, among the inhabitants of Barrow Straits, when introduced by the frozen-in whalers and the relief party, is sufficient disproof of any claim of special insusceptibility. There can be no doubt that in this, as in other virulent diseases, the rule holds that the long absence of the infection secures the preservation of the susceptible lines of blood, so that when the contagion does come it finds a more inviting field than in countries in which the more susceptible strains have been killed off and the comparatively immune have survived. Toward the Arctic circle the Indian must crowd into closer quarters in winter than his brother further south; but, in spite of all, the beef-eating Indian is being rapidly exterminated by tuberculosis, to which his brother of the north is a comparative stranger.
Exceptions: Their Explanation. This statement would be incomplete without a notice of exceptions to the rule. The Cape Town branch of the British Medical Association reports “that tuberculosis is rapidly increasing there in the human population, while tubercle in cattle is almost nonexistent.” This finds an abundant explanation in the different conditions of life. The men live indoors and concentrate the infection, whereas the cattle enjoy an outdoor life and escape. In a latitude of 30° south, where frost is rare, and with a dry climate (12 to 30 inches of rain per annum), the colonists find no occasion for housing their cattle, so that the conditions for the prevention of tuberculosis are ideal. It may be added that cattle are far less numerous in Cape Colony than they formerly were. The destruction first by lung plague and later by rinderpest has made the cattle industry extremely hazardous, and even before the advent of the rinderpest many had abandoned cattle and taken to sheep.
Parallel cases can be found in other countries. In Egypt, the great resort of consumptives, cattle are almost immune, the abattoirs furnishing about one tuberculous ox in ten thousand killed.[[7]] From Tunis (Alix), Algiers (Sarciron, Plaise), and Senegambia (Lenoir) a similar testimony comes. Cattle imported from Europe may die of tuberculosis, which is liable to assume a rapidly fatal type; but the native cattle, kept in the open air, are practically exempt.