278 THE TISSUES AND MECHANISMS OF DIGESTION. 



After death, the stomach is frequently found partly 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 shown by the fact that the leg of a living frog or the ear of 

 a living rabbit introduced into the stomach of a dog, through a gastric 

 fistula, is 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 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 themselves. We might add, it does 

 not explain why the amoeba, while dissolving the protoplasm of the swal- 

 lowed diatom, does not dissolve 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 the entrance into itself by 

 osmosis of more water than it requires to carry on its work, while a few 

 moments after it is dead water enters freely by osmosis, and the effects of 

 that entrance become abundantly evident by the formation of bullse and 

 the breaking up of the protoplasm. 



THE PROPERTIES AND CHARACTERS OF BILE, PANCREATIC JUICE, AND 



Succus ENTERICUS. 



213. In the living body the food, subjected to the action first of the 

 saliva and then of the gastric juice, undergoes in the stomach changes which 

 we shall presently consider in detail, and the food so changed is passed on 

 into the small intestine, where it is further subjected to the action of the bile 

 secreted by the liver, of pancreatic juice secreted by the pancreas, and pos- 

 sibly to some extent, though this is by no means certain, of a juice secreted 

 by the intestine itself and called succus entericus. It will be convenient to 

 study the minute structure of the liver in connection with other functions 

 of the liver more important, perhaps, than that of the secretion of bile, 

 namely, the formation of glycogen, and other metabolic events occurring 

 in the hepatic cells ; we have already studied the structure of the pan- 

 creas ; and the structure of the intestine will best be considered by itself. 

 We, therefore, turn at once to the properties and characters of the above- 

 named juices. 



Bile. 



Though bile, after secretion in the lobules of the liver, is passed on 

 along the hepatic duct, it is in the case of most animals not poured at once 

 into the duodenum, but taken by the cystic duct to the reservoir of the gall- 

 bladder. Here it remains until such time as it is needed, when a quantity 

 is poured along the common bile duct into the intestine. 



The quality of bile varies much, not only in different animals, but in 

 the same animal at different times. It is, moreover, affected by the length 

 of the sojourn in the gall-bladder; bile taken direct from the hepatic duct, 

 especially when secreted rapidly, contains little or no mucus ; that taken 

 from the gall-bladder, as of slaughtered oxen or sheep, is loaded with mucus. 

 The color of the bile of carnivorous and omnivorous animals, and of man, 

 is generally a bright golden red ; of herbivorous animals, a yellowish green 

 or a bright green or a dirty green, according to circumstances, being much 

 modified by retention in the gall-bladder. The reaction is neutral or alka- 

 line. The following may be taken as the average composition of human 



