244 DIGESTIVE SYSTEM. 



these fatty matters. The amylaceous substances are changed 

 into dextrine, and saccharized in the stomach, by means of 

 the saliva which is swallowed with the food. The quantity 

 of saliva varies according to the continuation of mastication 

 a longer or a shorter time : thus when the digestion is im- 

 peded, a larger or smaller quantity of saliva is finally swal- 

 lowed, and this assists the action of that which was swallowed 

 with the food. This helps us to understand the difficulty, 

 in artificial digestion, of operating upon the gastric juice 

 alone, or unmixed with saliva. 



The albuminoid substances, finally, belong essentially to 

 the province of the gastric juice, and to that alone (we are 

 not now speaking of the intestinal juices). If a piece of 

 muscular flesh be placed in contact with the saliva, it quickly 

 putrefies ; while if the same experiment be made with the 

 gastric juice, the meat is preserved, and even putrefaction, 

 which has already begun, arrested. The saliva thus evi- 

 dently has no effect upon this class of aliments. The prop- 

 erty possessed by the gastric juice of arresting decomposition 

 was first observed by Spallanzani, and several surgeons have 

 attempted to make use of it, in arresting the putrefaction of 

 wounds. The odor of the stomach of those animals which 

 feed on carrion is not more powerful than that of others, 

 even after the ingestion of meat which is very strongly 

 tainted. 



The most remarkable effect produced on albuminoid sub- 

 stances by the gastric juice is the transformation which they 

 undergo. Those which are fluid are changed into another 

 fluid, more absorbable, and which does not coagulate under 

 ordinary reactions. Thus the white of egg, when mixed 

 with the gastric juice, becomes fluid like water. Casein 

 alone, when brought into contact with the gastric juice, coag- 

 ulates before disappearing : this property is made use of in 

 curdling milk, by means of the pepsin contained in the pre- 

 served stomach of a calf (rennet) . 



The solid albuminoid substances, either before ingestion, 

 or when coagulated by pepsin, like casein, are liquefied by 

 the gastric juice. To this process there are two stages. 

 The albuminoid substance, a small cube of the white of egg, 

 for instance, first swells; its edges then lose their regular 

 outline, and it is finally reduced to a tenuous powder : in the 

 first stage, no part is really dissolved ; such porphyration 

 or crumbling occurs as would be produced by mechanical 

 action, and yet it is simply owing to the action of the gastric 



