INFECTIONS OF THE DIGESTIVE TRACT 77 



ance of the microscopical fields and the gas production 

 in the fermentation tubes. These conditions of bacterial 

 activity in the period of senility are like those which 

 were just described a& being common in people about the 

 age of fifty. The main difference between the putrefac- 

 tive conditions found at fifty and at seventy is that at 

 the latter period they are a little more marked in their 

 intensity and affect a much larger proportion of the pop- 

 ulation. The subjects in question at this later period 

 of life are not ill, but in order to keep fairly well have to 

 be very careful as to their habits of living. They are 

 moderately anaemic and easily develop slight disorders 

 of digestion. They weigh less than formerly, and though 

 they may still be well nourished in appearance, are con- 

 scious of losing strength from year to year. They are 

 undergoing what is usually regarded as normal involution. 

 Thus it is clear that there exists a distinct difference 

 between normal childhood and adolescence on the one 

 hand and normal old age on the other in respect to the 

 intensity of the putrefactive processes that go on in the 

 digestive tract. The origin and precise significance of 

 this difference are at present not clear. It appears 

 likely that the tendency to an increasing degree of putre- 

 factive decomposition in the intestine is connected with 

 the repeated but not necessarily severe derangements 

 of intestinal function that are experienced from time to 

 time by most individuals. In the course of these acute 

 derangements, there is frequently an increased opportu- 

 nity for the development of putrefactive anaerobes, and 

 it is possible that owing to slight but persistent damage 



