54 INFECTIONS OF THE DIGESTIVE TRACT 



first infection of the digestive tract to necessary bacterial 

 inhabitants of the milk. But since a portion of the 

 milk may come in contact with the nipple, and the child's 

 lips come into contact with the skin of the breast as well 

 as the surface of the nipple, it is clear that any bacteria 

 living on or near the nipple may find their way into the 

 digestive tract of the child. It might be supposed that 

 the gastric juice or the enterokinase of the small intes- 

 tine would form an obstacle to the passage of living bac- 

 teria into the intestine, but it has been well demonstrated 

 that these defenses even in the fully developed form in 

 which they exist in adults, are only partial, and that many 

 living bacteria readily pass from the stomach into the 

 small intestine in newly born children. In the case of 

 very young children, the secretion of a bactericidal gastric 

 juice is probably but a feeble protection against the pas- 

 sage of living bacteria into the intestine, and even were 

 it in part effective, there might frequently be oppor- 

 tunity for bacteria, located in the interior of curds, to 

 pass from the stomach into the intestine. Moreover, 

 if the bacteria were present in large numbers in the stom- 

 ach, some of them would almost certainly pass into the 

 intestinal tract, although, as has already been seen in 

 discussing the distribution of the bacteria of the intes- 

 tinal tract, it is usual to observe a considerable falling 

 off in the numbers of microorganisms as one passes from 

 the stomach to the duodenum and jejunum. It seems 

 probable, then, on the grounds already stated, that an 

 infection of the intestine by bacteria occurs through the 

 mouth. This probability was rendered a certainty by 



