The percentage of tuberculous animals recorded at the slaughterhouses of Berlin in 1892–1893 was as follows: Cows and oxen, 15.1; swine, 1.55; calves, 0.11; sheep, 0.004. Similar records at Copenhagen in 1890–1893 give the following result: Cows and oxen, 17.7; swine, 15.3; calves, 0.2; sheep, 0.0003. The order of the animals is the same, and it is confirmed by other slaughterhouse statistics; but the discrepancies between the figures indicate considerable variation in frequency, and only allow general conclusions to be drawn. A striking fact is the comparatively small amount of tubercle in calves. It shows, as Nocard has pointed out, that heredity cannot play an important part in the transmission of bovine tuberculosis. The infrequency of the disease in sheep is attributed to the open-air life they lead, and no doubt that is an important factor. The more animals and persons are herded together and breathe the same air in a confined and covered space, the more prevalent is tuberculosis among them. Stefansky found the disease in 5% of the rats caught in Odessa, and Lydia Rabinowitch obtained similar results in rats caught in Berlin. But there are evidently degrees of natural resistance also. Horses are more confined than cattle in the United Kingdom, yet they are far less affected; and on the other hand, cattle running free in the purest air may take the infection from others. Professor McEacharn of Montreal states that he has seen tuberculosis prevalent in ranch cattle, few of which were ever under a roof, ranging on the foothills of the Rocky Mountains in Montana. In cows and monkeys the lungs are chiefly affected; in horses and pigs the intestine and abdominal organs.
The relation between human and animal tuberculosis has been much debated. The bacillus in man very closely resembles that found in other mammalia, and they were considered identical until Koch threw doubt on this view at the British Congress on Tuberculosis in 1901. The British government thereupon appointed a royal commission to inquire into the relations of human and animal tuberculosis. The second interim report of the commission was issued in 1907, and the conclusions arrived at in it are: “ That there seems to be no valid reason for doubting the opinion, never seriously doubted before 1901, that human and bovine bacilli belong to the same family. On this view the answer to the question, Can the bovine bacillus affect man? is obviously in the affirmative. The same answer must also be given to those who hold the theory that human and bovine tubercle bacilli are different in kind, since the ' bovine kind ' are readily to be found as the causal agents of many fatal cases of human tuberculosis.” The commission also found that there is an essential unity not only in the nature of the morbid processes induced by human and bovine tubercle bacilli, but also in the morphological characteristics exhibited by the tubercle bacilli which cause these processes. The conclusions of the members of the Paris Congress on Tuberculosis, held in 1905, are: “ That human tuberculosis can be transferred to the bovine animal, and that what is termed the bacillus of bovine origin can be discovered in the human subject, and that there is a possibility that they may be varieties of one species.”
The distribution of tuberculosis is universal, and it is coincident with Distribution and Mortality. the existence of the human race in the habitable regions of the globe. Its comparative absence in the Arctic regions seems more due to the sparsity of population than to climatic effect. Indeed, it has been shown that climate has much less effect in its prevalence than has been formerly thought to be the case, the conclusion of Hirsch being that “ the mean level of the temperature has no significance for the frequency or rarity of phthisis in any locality.” The nature of the occupations and the density of population in any given area tend to its increase or otherwise, and the comparative immunity enjoyed by uncivilized races is due to their open-air life and to the sanitary advantages derived from the comparatively frequent changes of the sites of their camps and villages. Segregation of these races in fixed areas has shown an increased incidence of tuberculosis, and when living under civilized conditions they fail to exhibit any natural immunity. Altitude has an apparent influence on the frequency of phthisis, the rarity of the disease at high altitudes in Switzerland having been demonstrated, and a like protective influence is enjoyed by certain elevated districts in Mexico, notwithstanding the insanitary conditions of the towns thereon. The protection afforded by the altitude is alleged to be due to the dryness of the atmosphere, its freedom from impurities and the increased solar radiation. While no race is exempt from tuberculosis, certain races afford a greater case incidence. E. Baldwin states that the mortality from consumption in recently immigrated races in the United States is much greater than in those of longer residence. It was found that among those whose mothers were of foreign birth the rate was—in Russians 71.8, Germans 167, Scottish 172.5, French 187.7 and Irish 339.6, while in native-born Americans it was 112.8. The well-known susceptibility of the Irish has been attributed to the moisture of the climate, under-feeding, and the residual inferiority of a population drained by the emigration of a large number of able-bodied adults. That there is some added factor is shown by the fact that the above mortality of 339 in those having Irish mothers, in 1901, was greater by 31% than that of the Irish in Ireland at the same period. The Jews are said to show a relative immunity, but the matter requires further investigation. The factor which seemingly has the most constant influence on the mortality from tuberculosis is density of population. A high rate of mortality occurs in connexion with overcrowding and bad ventilation in cities, and it is proved that the death-rate from this disease is considerably lower in the country than in the towns. In addition, when we consider that it does not occur in epidemics or at certain seasons, but is constantly active, it will easily be seen that no other disease is so destructive to the human race. At the Tuberculosis Congress, held in Paris in 1905, it was stated by Kayserling that one-third of all deaths and one-half the sickness amongst adults in Germany was due to tuberculosis.
In 1908 the mortality from all forms of tuberculosis in England and Wales was, according to the registrar-general's returns, 56,080, less by 3455 than the average of the previous five years, being equal to 10.8% of the mortality from all causes, while in Ireland in 1909 14% of the total mortality was assigned to it. The following table gives the comparative mortality from pulmonary tuberculosis for certain fixed years together with the estimated population of certain selected countries:—
| Estimated Population in Years. | Mortality from Pulmonary Tuberculosis. | |||||
| 1892. | 1900. | 1907. | 1892. | 1900. | 1907. | |
| England and Wales | 29,760,842 | 32,249,187 | 34,945,600 | 43,323 | 42,987 | 39,839 |
| Ireland | 4,633,808 | 4,468,501 | 4,377,064 | 10,048 | 10,076 | 8,828 |
| German Empire | 47,125,446 | 52,624,706 | 61,994,743 | 113,720 | 108,827 | 97,555 |
| France | 38,360,000 | 38,900,000 | 39,222,000 | 31,080 | 34,357 | 40,304 |
| Norway | 2,010,000 | 2,211,300 | 2,305,700 | 3,358 | 4,249 | 4,656 |
| Italy | 30,665,662 | 32,346,366 | 33,776,087 | 39,715* | 41,733* | 41,968* |
| Holland | 4,645,660 | 5,159,347 | 5,709,755 | 8,906 | 8,451 | 7,403 |
| Belgium | 6,195,355 | 6,693,548 | 7,317,561 | 10,491 | 9,117 | 7,377 |
| Switzerland | 3,002,263 | 3,299,939 | 3,525,290 | 5,785 | 6,692 | 6,063 |
| * In Italy the mortality given is for all forms of tuberculosis. | ||||||
We thus see there is a general tendency to decrease in the death-rate, with the possible exception of France and Norway. In England the decrease has been most marked, having fallen from 3457 per million living in 1851–1860, or 15.6% of all deaths, to 1583 per million living, or a mortality of 10.8% of the death-rate from all causes for all ages and sexes.
| 1860. | 1870. | 1880. | 1890. | 1900. | 1908. | |
| Males | 3300 | 3300 | 2900 | 2700 | 2200 | 1800 |
| Females | 3300 | 3000 | 2500 | 2100 | 1600 | 1350 |
| Both Sexes | 3300 | 3150 | 2700 | 2400 | 1900 | 1583 |
