INFECTIONS OF THE DIGESTIVE TRACT 33 



human intestine and in that of dogs is much increased 

 in the ileum as compared with higher levels. Hence 

 we find that the mixed faecal bacteria taken from this 

 level of the lower ileum are capable of inducing putre- 

 factive changes in native proteids and in more simple 

 nitrogen-holding media. This is true of the human ileum 

 in health and at all periods of life, but the accumulation 

 of putrefactive bacteria is even more pronounced in 

 certain cases of disease in other words, anaerobic con- 

 ditions of bacterial life are exaggerated in pathological 

 states. We may indeed look on the ileum as the debat- 

 able land of the digestive territory. In ideal health 

 this region contains relatively few anaerobes and patho- 

 genic bacteria; in acute and chronic intestinal patho- 

 logical processes the ileum is probably inhabited by 

 flora capable of producing substances which may 

 damage the organism either locally or generally, and 

 among these the anaerobes are apt to be prominent. 



In the large intestine we find the most dense accumu- 

 lation of bacteria and the best conditions for anaerobic 

 growth. The transition from small to large intestine 

 is in this respect very striking, more regularly so, per- 

 haps, in dogs than in human beings. In dogs the large 

 intestine is usually closely crowded with bacteria beyond 

 the ileocaBcal valve, whatever may be the conditions in 

 the ileum. The anaerobic conditions are well main- 

 tained throughout the large intestine, and it is here that 

 we find the greatest numbers of anaerobes and the most 

 pronounced evidence of putrefaction. There is, however, 

 a gradual fall hi the number of living bacteria beyond the 



