330 A MANUAL OF PHYSIOLOGY 



warn us not to conclude that the power of forming ferments 

 belongs exclusively to any class of cells. And it is possible 

 that food-substances absorbed from the blood are further 

 elaborated by ferment action within the tissues themselves ; 

 while many facts show that the power of contraction is 

 widely diffused among structures whose special function is 

 very different, and a few point to its possession in some 

 degree even by glandular epithelium. On the other hand, 

 it must be remembered that none of the digestive glands 

 absorb food directly from the alimentary canal to be then 

 digested within their own cell-substance ; the ferments 

 which they form do their work outside of them ; their cells 

 feed also upon the blood. 



Why are the Tissues of Digestion not affected by the Digestive 

 Ferments ? This is the place to mention a point which has 

 been very much debated, though never satisfactorily ex- 

 plained : Why is it that the stomach or the small intestine 

 does not digest itself? This is really a part of a wider 

 question : Why is it that living tissues resist all kinds of 

 influences, which attack dead tissues with success ? The 

 living leucocyte destroys bacteria by which the dead 

 leucocyte is broken up ; it kills and digests them by sub- 

 stances formed within itself, but its own living protoplasm 

 is not digested. Or if the battle goes the other way, the 

 bacteria kill the leucocyte, and break it up, perhaps, by the 

 aid of ferments of their own manufacture which affect it but 

 not them. The amoeba digests food in its cell-substance, 

 but does not digest itself. The pancreatic juice acts with 

 great intensity upon proteids, but not upon the proteids of 

 the living pancreas and the living intestinal wall. When we 

 ascribe these things to the resistance of living tissues, we 

 play with words. And we have to inquire whether this is a 

 general resistance of all living tissues, or a specific resistance 

 of certain tissues to certain influences. 



That all living tissues cannot withstand the action of the 

 gastric juice has been shown by putting the leg of a living 

 frog inside the stomach of a dog ; the leg is gradually eaten 

 away (Bernard). It is true that it has first been killed and 

 then digested, but the question is, why the stomach-wall is 

 not first killed and then digested ? When the wall has been 



