520 Tuberc-ulnsis. 



suffered a slight or passing attack of the disease and thus 

 acquired a certain immunity which was later perhaps intensified 

 by repeated infections at longer or shorter intervals of time. 



The dissemination of tuberculosis was formerly explained 

 by assuming special individual and a family predisposition. 

 In human beings this was supposed to find expression in a 

 IjTiiphatic constitution ; and in an improper development of the 

 thorax (flat and norrow chest, hal)itus phthisicus). As far as 

 our domestic animals are concerned there is no foundation upon 

 which to base such a supposition and the great regularity with 

 which we find the disease in all large herds points against the 

 correctness of this view. It is true that the disease is especially 

 prevalent in certain families or strains but this may readily be 

 explained by the uniformly favorable conditions for infection. 



Formerly individual predisposition was supposed to lie due to a 

 slight power of resistance on the part of the body to the tuberculous virus 

 as well as to an unfavorable constitution and to hypoplasia of the blood 

 vessels. According to Baumgarten tuberculosis of human beings is 

 usually congenital in the sense that the offspring is born with tubercle 

 bacilli in its system, where they remain latent until tliey develop and 

 produce active disease perhaps only after years under the deleterious 

 influence of various agencies. Tuberculosis of the lymphatic glands and 

 of the bones especially was supposed to originate in this manner. 



The existence of such long-continued latency is contradicted by the 

 common observation that the human hody is, especially in its earliest 

 infancy, highly susceptible to tuberculosis and that the disease then as 

 a rule runs a rapid and fatal course. According to Behring the pre- 

 disposition to tuberculosis is attributed to an infection in early youth, 

 resulting in disease of the lymph glands (scrophulosis) which, by the 

 destruction of certain lymphatics and their glands and the production 

 of changes in the walls of blood vessels, produces a hypersensitiveness to 

 tuberculin, and that involvement of the thoracic lymph glands gives 

 rise to an abnormal development of the thorax by affecting the sternal 

 articulations. According to this view an individual predisposition would 

 not be congenital but rather ac(|uired and could be guarded against by 

 the preventing of extra-uterine infection in early life. But this view 

 must be objected to on the same grounds as the former. As a matter of 

 fact, we can not as yet offer a satisfactory explanation for individual 

 predisposition, the existence of which cannot be denied. 



After careful study of the herd registers of the estate Weidlitz, coverinpf a 

 period of .59 years, Hermann concluded that in all cases of tuberculosis in this 

 herd one of the following predisposing causes could be established ; late born 

 calves in large families, lack of fresh air and of proper exercise, inbreeding, 

 tuberculous parents. 



Heredity plays no very important role in predisposition 

 nor in the dissemination of tuberculosis in general. Although 

 tuberculosis may be directly transmitted from the mother to 

 the unborn calf, as has been demonstrated by the actual ob- 

 servation of well developed disease in the newborn animal, such 

 cases are very rare and occur only when the uterus itself or 

 the cotvledons are diseased. Aside from this, animals born 



