160 DIGESTION. 



up, becomes transparent and gelatinous, and after a time dissolves. 

 The same effect is produced, though more slowly, upon hard-boiled white 

 of egg. The solid caseine of cheese is liquefied and the oleaginous 

 particles set free. This action is in every case more or less dependent 

 upon the temperature. It is entirely suspended at or near the freezing 

 point, but becomes more and more active with the increase of warmth, 

 and is most energetic from 35 to 40 (about 100 P.). Above that 

 point its activity again diminishes, and at a boiling temperature it is 

 entirely destroyed. It is owing to the influence of temperature that 

 digestion is more slowly performed in the cold-blooded reptiles than in 

 the warm-blooded birds and quadrupeds. This difference has been 

 shown by Schiff, 1 who made acidulated infusions of the stomachs of two 

 serpents, and placed in each the same measured quantity of coagulated 

 albumen ; one of the infusions being allowed to remain at a temperature 

 varying from 10 to 11 (50 to 62 F.), the other being introduced, in a 

 closed glass tube, into the stomach of a living dog. The second was 

 found to have digested in six hours as much albumen as the first at the 

 end of three weeks. 



The changes produced in solid albuminous matters during digestion 

 by gastric juice are as follows: The first effect is a swelling and gela- 

 tinization of the substance under the influence of the free acid. This 

 will take place by the action of a dilute acid alone, and with the aid of 

 continuous warmth a part of the substance will after a time even be 

 dissolved. This solution, however, is not a true digestion of the albu- 

 minous body. It has merely been modified in such a way as to be 

 soluble in an acidulated liquid, and it may be again precipitated by 

 neutralizing the solution by means of an alkali or an alkaline carbonate. 

 This modification of the albuminous matter, however, by the action of 

 the free acid, seems to be an essential preliminary in the digestive act. 

 If it be allowed to go on farther, the influence of the pepsine produces 

 a more important change, by which the original substance is converted 

 into albuminose. In this form it is no longer precipitable by neutral- 

 ization of the fluid, and has consequently become soluble in water. It 

 is not coagulable by boiling, either in a neutral, acid, or alkaline liquid ; 

 and it is not precipitable by nitric acid or by potassium ferrocyanide, 

 although it may still be thrown down by alcohol in excess. It has thus 

 become essentially altered in its chemical relations. 



An equally or even more important change has also taken place in 

 its physical characters ; that is, it has acquired the property of diffusi- 

 bility. The other liquid albuminous matters, as albumen, caseine, 

 mucosine, and the like, do not pass through parchment paper or the sub- 

 stance of an animal membrane ; or they pass, if at all, very slowly and 

 in small quantity. Even pepsine is retained in this way almost com- 

 pletely by such a membrane. Albuminose, on the contrary, diffuses 

 itself with great readiness through membranous partitions, and can be 



1 Lecons sur la Physiologic de la Digestion. Paris, 1867, tome ii. p. 19. 



