276 DIGESTION. 



solution, is obtained in a greyish-brown viscid fluid. The 

 addition of alcohol throws down the pepsin in greyish- 

 white flocculi ; and one part of the principle thus prepared, 

 if dissolved in even 6o,OOO parts of water, will digest meat 

 and other alimentary substances. 



The digestive power of the gastric fluid is manifested in its 

 softening, reducing into pulp, and partially or completely 

 dissolving various articles of food placed in it at a tempe- 

 rature of from 90 to I OO. This, its peculiar property, 

 requires the presence of both the pepsin and the acid ;. 

 neither of them can digest alone, and when they are 

 mixed, either the decomposition of the pepsin, or the 

 neutralization of the acid, at once destroys the digestive 

 property of the fluid. For the perfection of the process 

 also, certain conditions are required, which are all found 

 in the stomach ; namely ( i ), a temperature of about 

 I OO F. ; (2), such movements as the food is subjected to 

 by the muscular actions of the stomach, which bring in 

 succession every part of it in contact with the mucous 

 membrane, whence the fresh gastric fluid is being secreted ; 

 (3), the constant removal of those portions of food which 

 are already digested, so that what remains undigested may 

 be brought more completely into contact with the solvent 

 fluid ; and (4) a state of softness and minute division, such 

 as that to which the food is reduced by mastication previous 

 to its introduction into the stomach. 



The chief circumstances connected with the mode in 

 which the gastric fluid acts upon food during natural diges- 

 tion, have been determined by watching its operations 

 when removed from the stomach and placed in conditions 

 as nearly as possible like those under which it acts while 

 within that viscus. The fact that solid food, immersed in 

 gastric fluid out of the body, and kept at a temperature of 

 about I OO, is gradually converted into a thick fluid similar 

 to chyme, was shown by Spallanzani, Dr. Stevens, Tiede- 

 mann and Gmelin and others. They used the gastric fluid 



