420 Chapter XIII 



juice of the dog destroys relatively small quantities of the diphtheria 

 poison. A gramme of the juice is capable of rendering innocuous 

 50 lethal doses of this toxin, but, in order that this action may be 

 produced, a prolonged contact of the two substances is required. 

 Since the neutralised gastric juice acts in the same way, this effect 

 must be attributed not to the acidity of the gastric juice, but rather 

 to the amount of pepsin it contains. This diastase acts much more 

 powerfully on the tetanus toxin, 1 gramme of gastric juice neutral- 

 ising 10,000 doses lethal for the guinea-pig. On the other hand, 

 abrin is not modified by the gastric juice according to the researches 

 of Repin^, carried out in Roux's laboratory. Nevertheless, its action 

 when administered by the stomach is feeble, and Ehrlich^ has been 

 enabled to vaccinate small animals against this vegetable poison by 

 availing himself of his knowledge of this fact. Repin explains this 

 result as due to the very slight absorption of abrin by the gastro- 

 intestinal mucous membrane. This same factor, R6pin thinks, may 

 contribute also to the failure of various toxins when ingested. This 

 rule, however, is not an absolute one. Thus, the toxin of the botu- 

 linic bacillus of van Ermengem^ is not destroyed by the digestive 

 diastases, and it is certainly absorbed by the mucous membrane of 

 the alimentary canal. For this reason, when it is introduced by way 

 of the stomach, it exhibits a very violent toxic activity. 



The stomach, though capable, through its acid, of preventing 



[441] the multiplication of certain micro-organisms, protects, very feebly, 



the rest of the digestive apparatus. As soon as, in the duodenum, 



the acidity is weakened or neutralised, the various micro-organisms 



commence to multiply and soon develop very abundantly. 



In the animal series the intestine proper presents a very great 

 variability, and even, in closely allied species, exhibits considerable 

 differences. From the particular point of view which interests us 

 these differences are very marked. Alongside insects, such as the 

 silkworm, the larvae of cockchafers and others, whose intestinal canal 

 contains a very rich bacterial vegetation, we have others which contain 

 exceedingly few micro-organisms or, indeed, none at all. This last 

 condition is represented by the caterpillars of small Lepidoptera, and 

 notably by those of several species of clothes-moths. These differences 

 correspond to the variety of the juices and digestive ferments met with 



^ Ann. de VInst. Pasteur, Paris, 1895, t. ix, p. 517. 



2 Deutsche med. Wchnschr., Leipzig, 1891, SS. 976, 1218. 



3 CentralU.f. Bakteriol u. Parmitenk., Jena, 1896, Bd. xix, S. 442. 



