Tuberculosis in Cattle. 9 



the breath of the tuberculous is not in itself infecting, and if 

 care is taken to prevent the diffusion of the infected solids and 

 liquids and their distribution in dust, the presence of a tubercu- 

 lous individual is not a threat to others adjacent. 



2. hifection through food and drink. A whole host of experi- 

 menters have conveyed the disease by mixing infecting pus or 

 an emulsion of the tubercle with ordinary food. The same has 

 been often accomplished with milk from the infected animal 

 even to cases in which the mammar}^ glands seemed to be per- 

 fectly sound. The danger of course is enhanced in ratio with 

 the number of bacilli present, so that one diseased cow in a large 

 herd leads to little infection if the milk of the whole herd is 

 mixed. On the other hand such admixture of the virulent milk 

 with the wholesome contaminates the whole to some extent, and 

 inoculation with such mixed milk will often convey the disease 

 when the animals drinking it do not seem to be injured by it. 



The infection usually takes place through the tonsils, 

 pharynx or bowels. In ruminating animals it may attack the 

 first three stomachs the contents of which are neutral or nearly 

 so, but it rarely attacks the true digesting stomach the secretion 

 of which is strongly acid. The bacillus is liable to perish or to 

 be so distributed by the acid in passing through the stomach that 

 it is largeh^ shorn of its danger. Among the conditions that 

 favor its safe passage through the stomach may be named indi- 

 gestion and a too rapid progress of the undigested food through 

 the stomach, a condition which is especially common in young 

 animals: overloading of the stomach: the ingestion of an excess 

 of cold water just after a meal, thereb}^ rousing excessive ver- 

 micular movement of the stomach and premature expulsion of its 

 undigested contents: and the enclosure of the infected matter in 

 a mass of fat which the gastric secretions are impotent to digest 

 or emulsion ize. 



3. hioculatioyi inwoiuids. This is a common channel of in- 

 fection in man. Accidental inoculations — in making post mor- 

 tem examinations have been often noticed since the case of 

 lysennec ; or in making artificial cultures in the laboratory ; or 

 in washing the clothes of tuberculous persons ; or in dressing 

 the tuberculous sores ; or in making operations, notabl}^ that of 



