Preliminary remarks on immunity m animal kingdom 59 



several stages of this evolution so that in the higher representatives of 

 the group, such as the slugs and the snails, we meet with digestion 

 carried on only by secreted juices in the gastro-intestinal contents. 

 In these Mollusca a voluminous glandular organ, the liver, which is . 

 certainly derived from coecal appendices similar to those of Phyllirhoe, 

 is now met with. Regarded from this point of view the liver is, as 

 Claude Bernard has stated, an organ of second digestion. I think 

 that a detailed study of the liver of the Mollusca, guided by this idea, 

 will give results of considerable importance. 



In the Vertebrata intracellular digestion in the gastro-intestinal 

 canal almost disappears and is replaced by digestion carried on 

 by means of ferments contained in secreted juices. We cannot, of 

 course, offer to the reader anything like a complete account of 

 this extracellular digestion in the higher animals. It is necessary, 

 however, to draw attention to several aspects of this function which 

 have been established, thanks to the progress made during recent 

 years, in obtaining digestive juices and in the study of their action. 



For the study of intracellular digestion the sea-anemone is the 

 most suitable animal for our purpose ; for that of extracellular 

 digestion the dog. In this latter animal, an omnivorous flesh-eater, 

 the food-substances are treated by digestive juices of great activity 

 which contain a whole series of soluble ferments. The stomach 

 secretes two of these : rennet and pepsin. The pancreas elaborates 

 three : trypsin, amylase and saponase, which act on the three main 

 groups of food-substances. To these the small intestine adds a special 

 ferment, described by Pawloff 1 under the name of enterokynase. 

 Every one recognises the proteolytic function of pepsin and trypsin 

 and the analogies and differences between these two diastases. Nor 

 need I dwell on amylase or on the ferment which saponifies fats. But 

 enterokynase merits special attention in connection with the study of 

 immunity. Pawloff entrusted to his pupil Che"powalnikoff the study 

 of the digestive role of the intestinal juice concerning which, up to 

 this, very little was known. It was known indeed that this juice 

 contained weak saccharifying and inverting ferments, but it was [64] 

 generally regarded as a secretion of little importance. Chepowal- 

 nikoff 2 has demonstrated that this view is absolutely erroneous. The 

 intestinal juice fulfils the very important function of accelerating the 



1 Address delivered before the Societe des medecins russes at St Petersburg. 

 Gaz. din. de Botkine, 1900. 



2 " Physiologic du sue intestinal," Saint-Petersbourg, 1899 (Thesis, in Russian). 



