DIGESTION 359 



manufactured 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 neces- 

 sary 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 disproportionately 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 dis- 

 appears. But the presence of pepsin in the white blood-corpuscles, 

 the parasites as well as the scavengers of the blood, and of amylo- 

 lytic, proteolytic and lipolytic ferments in many tissues, should warn 

 us not to conclude that the power of forming ferments belongs ex- 

 clusively 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 

 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 ali- 

 mentary 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 

 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 ? 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 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), 



