AVENUES OF INFECTION 37 



with tuberculosis by inhalation, rarely or not at all by feeding. The 

 number of bacilli necessary to infect a guinea-pig by inhalation is 

 less than one one-thousandth of that necessary to infect by feeding. 

 When animals are infected by inhalation, the lesions can be detected 

 in the lungs long before they appear after feeding. 



The evidence that infection does result from inhalation and that 

 the primary seat of the infection is in the apices of the lungs in the 

 great majority of cases of pulmonary tuberculosis seems to be indis- 

 putable. On the other hand, it is equally certain that infection may 

 develop by way of the intestinal tract. The frequency with which 

 primary tuberculosis due to the bovine bacillus, occurs in the abdom- 

 inal organs of children leaves no room to question. The contention of 

 Koch that infected milk might be neglected in our attempts to eradi- 

 cate tuberculosis is not supported by the results of the most thorough 

 study that has been devoted to it. There is probably no avenue of 

 infection which has not been traveled by the bacillus tuberculosis. 



The Stomach. There is probably no specific infectious disease 

 which develops primarily in the stomach. Indeed, the acid secretion 

 of this organ, while by no means affording constant or full protection 

 against intestinal infection, undoubtedly does much in this direction. 

 The ubiquitous pus germ does develop a gastric ulcer now and then, 

 but a more favored site for this process is in the duodenum. In the 

 intervals between digestion all kinds of harmful bacteria may pass the 

 portals of this viscus in safety and some of them make a successful 

 passage even when digestion is at its height. It is not wise to depend 

 on the gastric juice to sterilize our food. 



The Intestine. There is general agreement that the intestine of 

 the infant is more permeable to bacteria than that of the adult. Young 

 guinea-pigs are easily infected with anthrax by feeding, while adults 

 are not. Even attenuated cultures will infect a larger number of the 

 young than virulent cultures will in adults. Like results have been 

 reached by experiments with tuberculosis. Platte fed guinea-pigs a 

 few days old and adults with tubercle bacilli, 80 per cent, of the former 

 and 30 per cent, of the latter became infected. Ficker found that 

 many bacteria easily penetrate the intestinal walls of suckling animals, 

 while they have no effect on adults. These facts correspond with 

 observations on the summer diarrheas of infants. Milk that proves 



