382 DIGESTION 



factured in the cell and those which seem by a less special and 

 laborious, though a selective, process to be passed through it from 

 the blood. Their practical absence from bile, and, as we shall see, 

 from urine, their relative abundance in pancreatic and scantiness 

 in gastric juice, point to a closer dependence upon the special 

 activity of the gland-cell than we can suppose necessary in the case 

 of the salts. 



Although it is in the cells of the digestive glands that the power of 

 forming ferments is most conspicuous, it is by no means confined to 

 them. It seems to be a primitive, a native power of protoplasm. 

 Lowly animals, like the amoeba, lowly plants, like bacteria, form ferments 

 within the single cell which serves for all the purposes of their life. 

 The ferment-secreting gland-cells of higher forms are perhaps only lop- 

 sided amoebae, not so much endowed with new properties as dispro- 

 portionately developed in one direction. The contractility has been 

 lost or lessened, the digestive power has been retained or increased; 

 just as in muscle the power of contraction has been developed, and 

 that of digestion has fallen behind. The muscle-cell and the cartilage- 

 cell are parasites, if we look to the function of digestion alone. They 

 live on food already more or less prepared by the labours of other cells ; 

 and it is a universal law that in the measure in which a power becomes 

 useless it disappears. But the presence of pepsin in the white blood- 

 corpuscles, the parasites as well as the scavengers of the blood, and of 

 amylolyti^, proteolytic and lipolytic ferments in many tissues, should 

 warn us not to conclude that the power of forming ferments belongs 

 exclusively to any class of cells. There is good and growing evidence 

 that food-substances absorbed from the blood are further decomposed 

 and, in turn, elaborated by ferment action within the tissues them- 

 selves; 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. Why is it that the stomach or the small intes- 

 tine 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 ? And we have to inquire whether the 

 immunity of the alimentary canal to the digestive juices is an 

 example of a general resistance of all living tissues to destructive 

 agencies, or a specific resistance of certain tissues to certain in- 

 fluences. 



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 



