64 DIGESTION OF GELATINE. 



As the alteration takes place from calorifacient to nutritive digestion, 

 the active fluid changes its chemical relations. In the mouth and duo- 

 denum, alkaline juices are resorted to ; in the stomach and coecum, acid 

 ones. Whenever there is an accidental inversion of these conditions, the 

 result correspondingly changes ; so when bile, which is alkaline, regur- 

 gitates into the stomach, the digestion of nutritive food is instantly ar- 

 rested. 



In each of these cases the object is the same: it is to obtain the nutri- 

 ent material under such forms that the absorbent vessels can readily take 

 it up ; this, as we have seen, often involves a metamorphosis of the ele- 

 ments of the food where mechanical subdivision would be insufficient. 

 Fibrin has to be brought into a soluble state, and, indeed, albumen itself 

 must be modified. If it has been taken uncoagulated or glairy, it be- 

 comes opalescent, and passes into the allied form known as albuminose. 

 In this condition it is neither precipitated by heat nor by nitric acid, 

 though it is by corrosive sublimate. The cause of this transformation 

 probably has reference to the relative facility with which albuminose can 

 transude into the venous capillaries compared with albumen. 



There is thus reason to suppose that the result of stomach digestion 

 is the reduction of the various nitrogenized constituents of the food to 

 the condition of albuminose. It is plain that fibrin must come into this 

 or some analogous condition, for it can not be absorbed as fibrin, and, ac- 

 cordingly, it is found that the blood of the gastric and mesenteric veins 

 abounds in albuminose. 



Intermediate between the classes of calorifacient and histogenetic food, 

 Case of gela- belonging, by its composition and conditions of digestion, to 

 tine - the latter, but by the function it discharges to the former, is 



gelatine, a nitrogenized substance. It appears to be always derived from 

 albumen, and any portion which may have been received in the food is 

 never directly assimilated or used for the fabrication of tissue, but solely 

 ministers to the production of heat. Though thus a calorifacient body, 

 its place of digestion is the stomach. After it has suffered the action of 

 that organ it has lost its power of gelatinizing, can no longer be precip- 

 itated by chlorine, nor give the leather precipitate with tannin. The use 

 of it under the form of jellies, soups, etc., is always attended with the ap- 

 pearance of an unusual quantity of urea in the urine, and hence the ad- 

 ministration of those domestic preparations, under an idea of their great 

 nutritive value, is to be looked upon as only a popular error. In an in- 

 direct way, however, under the conditions of restricted diet, usually met 

 with in the sick-room, gelatine doubtless maintains an interesting relation 

 to the albumenoid bodies in this, that it protects them from destruction 

 by undergoing oxidation itself, and so satisfying the requirements of the 

 respiratory mechanism ; for, were there not such a substance present to 



