62 Chapter HI 



We know that the Peyer's patches are lymphoid organs in which 

 are a large number of amoeboid mononucleated cells, and that these 

 elements are even capable of ingesting foreign bodies and of sub- 

 mitting them to intracellular digestion. It is therefore not at all 

 astonishing that Delezenne should have succeeded in finding entero- 

 kynase in the mesenteric glands of several Mammals (dog, pig, rabbit). 

 These glands, when treated by the method just mentioned, yield a 

 substance which assists the action of trypsin just as does the intestinal 

 juice. Having reached this point, Delezenne asked himself whether 

 the mononucleated white corpuscles, so closely allied to the mono- 

 nucleated cells of the lymphoid organs, may not also contain 

 enterokynase. With the object of settling this point he collected 

 exudates that were rich in mononucleated leucocytes ; in these also 

 he found this same soluble ferment. Moreover, the leucocytic layer 

 of the blood showed itself equally capable of increasing, very 

 energetically, the action of trypsin. 



The results of the old experiments carried out by Schiff and by 

 Herzen on the adjuvant role of the extract of the spleen in pancreatic 

 digestion, must without doubt be ranged alongside those we have just 

 indicated. In fact the mononucleated cells of the spleen, like those of 

 Peyer's patches and of the mesenteric glands, contain a substance 

 which acts like enterokynase. Delezenne has given us a definite 

 demonstration of its presence and action. 



In intracellular digestion it is the chemical side which has been 

 most difficult of demonstration. The purely physiological functioning, 

 the sensitiveness of the digestive cells and the amoeboid movements 

 [67] of their protoplasmic processes are, on the other hand, so manifest 

 that it has even been suggested that intracellular digestion should be 

 looked upon as a protoplasmic phenomenon purely vital in character. 



In extracellular digestion through the agency of secreted juices 

 we have a very different condition. Here the chemical side is the 

 striking feature, the physiological factor being veiled more or less 

 completely. Nevertheless, thanks to recent advances and above all 

 to the labours of PawlofF's disciples in St Petersburg, this problem 

 has been elucidated in a very remarkable fashion. 



The secretion of digestive fluids follows definite laws, the most 

 potent factor being the reflex action of the nervous system. To use the 

 expression of Pawloff, the study of the process of salivary secretion 

 has revealed a real psychology of these organs. You may fill the 

 mouth of a dog with small polished pebbles or with snow ; you may 

 pour into it very cold water the saliva will not flow. But merely 



