CHAP. i.J DIGESTION. 279 



idea that one effect of food is to ' charge ' the gastric cells with 

 pepsinogen, and that certain articles of food might be considered 

 as especially peptogenous, i. e. conducive to the formation of pepsin. 

 Such a view is tempting, but needs as yet to be more fully 

 supported by facts. 



Seeing the great solvent power of both gastric and pancreatic 

 juice, the question is naturally suggested, Why does not the 

 stomach digest itself? After death, the stomach is frequently 

 found partially digested, viz. in cases when death has taken place 

 suddenly on a full stomach. In an ordinary death, the membrane 

 ceases to secrete before the circulation is at an end. That there 

 is no special virtue in living things which prevents their being 

 digested is shewn by the fact, that the legs of a frog or the ear 

 of a rabbit introduced into a stomach through a fistula are readily 

 digested. It has been suggested that the blood-current keeps up an 

 alkalinity sufficient to neutralize the acidity of the juice in the 

 region of the glands themselves; but this will not explain why 

 the pancreatic juice, which is active in an alkaline medium, does 

 not digest the proteids of the pancreas itself, or why the digestive 

 cells of the bloodless actinozoon or hydrozoon do not digest them- 

 selves. We might add, it does not explain why the amoeba, while 

 dissolving the protoplasm of the swallowed diatom, does not dis- 

 solve its own protoplasm. We cannot answer this question at all 

 at present, any more than the similar one, why the delicate 

 protoplasm of the amoeba resists during life all osmosis, while a few 

 moments after it is dead, osmotic effects become abundantly evident. 



The secretion of bile needs a few additional words. The analogy 

 of the other glands and what we already know of the microscopic 

 changes in the hepatic cells, leads us to believe that the secretion 

 of even such a complex fluid as the bile is in the main the result of 

 the direct metabolic activity of the protoplasm of the hepatic cells. 

 And this view is supported by the fact that after extirpation of the 

 liver, no accumulation of the biliary constituents is observed to take 

 place during the few hours of life remaining to the animal after the 

 operation. Still the great complexity of the secretion introduces 

 several very important considerations. In the first place, the liver, 

 unlike the other digestive glands, has a double supply of blood; and 

 vain attempts have been made to settle by direct experiment the 

 question whether the hepatic artery or the vena portse is the more 

 closely concerned in the production of bile. Ligature of the 

 hepatic artery has sometimes had no effect on the secretion, some- 

 times has interfered with it. Sudden ligature of the vena portse at 

 once stops the flow of bile; but gradual obliteration may be effected 

 without either causing death or even interfering with the secretion, 

 anastomotic branches forming a collateral circulation, and thus 

 maintaining an efficient flow of blood through the liver. The 

 problem, which is probably a barren one, cannot be settled in this way. 



In the second place, the hepatic cells not only secrete bile, but, 



