Immunity of the skin and mucous membranes 423 



the small intestine destroyed such large numbers of vibrios. He 

 supposes that alongside a mechanical factor, such as the very active 

 peristaltic movement, there exist others, perhaps chemical processes, 

 capable of killing these micro-organisms. 



This question of the defensive action in the small intestine is, 

 consequently, far from being settled. The data collected indicate 

 merely that the problem is a very complex one. It has been shown, 

 however, that very virulent bacteria may pass through the digestive 

 canal not only without injuring the animal but even meeting their 

 own death in this organ. The anthrax bacillus, so fatal to mice and 

 guinea-pigs, may be swallowed by these animals without the slightest 

 danger to them. It may then be found in the small intestine, but not 

 in the large intestine, this proving that the gastric acidity is incapable 

 of destroying them outright To produce generalised anthrax by 

 way of the intestine, it was necessary that the animals should swallow 

 the spores of anthrax along with spiny plants, as in the experiments 

 of Pasteur and his collaborators 1 , or along with sand or powdered 

 glass. In these cases the intestinal lesions served as the port of 

 entry for the bacillus, the intact mucous membrane of the intestine [444] 

 preventing their penetration. Mitchell, in an unpublished work, 

 undertaken in my laboratory, succeeded in giving fatal anthrax to 

 guinea-pigs, even when he fed them with spores mixed with the 

 " crumb " of bread soaked in milk. During the whole period of the 

 experiment the animals took no food capable of producing lesions 

 of the wall of the intestine. But examples of infection under these 

 conditions are altogether exceptional. In the great majority of 

 instances the animals were not attacked. The same rule applies also 

 to many other micro-organisms, which can be ingested with impunity 

 although their inoculation into the blood and tissues sets up infections 

 which are inevitably fatal. Many animals may, without running the 

 least ri:*k, swallow large numbers of bacteria which in man produce 

 grave intestinal disease. Thus, it has never been possible to produce 

 typhoid fever regularly and with certainty in any of the species of 

 animals to which masses of typhoid coccobacilli were given by in- 

 gestion. We may recall the difficulties which so many investigators 

 have met with in inducing intestinal cholera in laboratory animals, 

 which are so refractory to Koch's vibrio. Only very young animals, 

 especially unweaned rabbits, are capable of contracting fatal intestinal 

 cholera, but these animals may contract it not only from the true 

 1 Compt. rend. Acad. d. sc., Paris, 1880, t. xci, p. 86. 



