142 INFECTION AND IMMUNITY. 



habitat. The gastric juice may render some bac- 

 teria harmless by digesting their toxins; one 

 gram of the gastric juice of a dog will neutralize 

 fifty fatal doses of diphtheria toxin, or 10,000 of 

 tetanus toxin, using the guinea-pig as the test 

 animal. On the other hand, the toxin of the bacil- 

 lus of botulism (causing a form of meat poison- 

 ing) seems to be uninfluenced by the stomach con- 

 tents, as the development of the intoxication indi- 

 cates. Vomiting is often a means of ridding the 

 stomach of toxic substances, including bacteria. 

 The stomach itself is exceptionally free from in- 

 fections. 



intestines. The bile is moderately bactericidal for some 

 germs, but, on the whole, the intestinal secretions 

 have low germicidal powers; this is indicated by 

 the fact that the colon contains many more bac- 

 teria than the duodenum. On the other hand, 

 the pancreatic juice destroys some toxins (diph- 

 theria, tetanus) more powerfully even than the 

 gastric juice. This ability of the pancreatic juice 

 to destroy toxic bacterial products may explain the 

 more frequent occurrence of enteritis in the ileum 

 than in the duodenum. The bile also has a neu- 

 tralizing power for some toxins. Although a num- 

 ber of pathogenic bacteria inhabit the intestinal 

 tract (colon bacillus, streptococci, etc.), they do 

 not often set up inflammatory processes in the 

 adult. The tissues become accustomed to their 

 presence. The pathogenic bacteria which do not 

 normally exist in the intestines are those which, 

 on introduction, are most likely to cause disease 

 (typhoid, cholera, dysentery, etc.). The intesti- 

 nal tract of the infant, on the other hand, is fre- 

 quently attacked by some micro-organisms (strep- 



