MODES OF INFECTION AND TRANSMISSION 329 



it to other cows. Cows infected with pulmonary tuberculosis also 

 swallow a considerable quantity of their sputum and disseminate the 

 bacilli through their feces, which may contaminate the fodder of 

 other cows. 



Ingestion. This is the most common mode of infection in hogs. 

 Its process through skimmed milk from tubercular cows, feeding 

 after infected cattle, and devouring tubercular offal or cadavers has 

 already been referred to. Tuberculosis is also contracted through 

 the intestinal tract by calves feeding on cows with either more or less 

 generalized tuberculosis or with udder tuberculosis. 



Von Behring has advanced a theory that tuberculosis in man is 

 almost always primarily an intestinal infection in which the tubercle 

 bacilli are taken into the body in early childhood with milk from 

 tubercular cows. The bacilli then remain latent in the abdominal 

 cavity, particularly in the mesenteric glands. Later they enter the 

 lymphatics or the blood circulation and find the lungs the most 

 favorable place for their development and the establishment of an 

 extensive tubercular process. Certain statistics have been produced 

 in opposition to von Behring's view. They show that among a large 

 number of pulmonary consumptives, only a very small percentage 

 was fed on cow's milk as infants, while the great majority was breast- 

 fed and had never even received very much cow's milk. A powerful 

 argument indicating that pulmonary tuberculosis is developed 

 independent of feeding with cow's milk is the following, which the 

 author has not found mentioned elsewhere. Most monkeys and apes 

 kept in zoological gardens die from pulmonary tuberculosis. Most 

 of these animals have been born in tropical or subtropical countries. 

 They have, of course, been breast-fed by mothers never sick of 

 tuberculosis in the wild state, and have probably, throughout their 

 lives, never had a drop of cow's milk. Yet in captivity these animals 

 almost invariably die of pulmonary tuberculosis which they contract 

 by inhaling moist floating particles of pulverized dust of dried human 

 tubercular sputum. Another very strong argument against the 

 ingestion theory of von Behring is furnished by the observation that 

 certain nations, among which pulmonary tuberculosis is very prevalent, 

 do not consume cow's milk nor keep cattle, tubercular or otherwise, 

 as domestic animals. The inhabitants of Japan and the Philippine 

 Islands which, for example, are such countries, keep water buffaloes, 

 or carabaos, as beasts of burden, but not as meat- or milk-producing 

 animals. There is no tuberculosis among these carabaos, and as the 

 cattle of the Western nations are not kept among the Eastern nations 

 named, they cannot have played any role in the great prevalence of 

 tuberculosis among the Japanese and the Filipinos, nor can the disease 

 of the lungs be traced back to an early infection with bovine tubercle 

 bacilli. 



Wounds. Wounds of the external surface play a relatively un- 

 important part in producing tubercular infections in man and animals. 



