DESTINATION OF NOX-AZOTIZED ALIMENTS. 153 



substances are reduced in the stomach to the form of albumen ; 

 which is the raw material out of which the various fabrics of 

 the body are constructed. But the rule holds good with re- 

 gard to these also, that by being made to feed constantly on 

 the same substance, boiled white of egg for instance, or meat 

 deprived of the principle that gives it flavour, an animal may 

 be effectually starved ; its disgust at the food being such, that 

 even if it be swallowed it is not digested. It is very interest- 

 ing to remark that, in the only instance in which Nature has 

 provided a single article of food for the support of the animal 

 body, she has mingled articles from all the three preceding 

 groups. This is the case in Milk ; which contains a consider- 

 able quantity of the albuminous substance, casein, that forms 

 its curd ; a good deal of oily matter, the butter ; and no in- 

 considerable amount of sugar, which is dissolved in the whey. 

 The proportions of these vary in different Mammalia, being 

 related as it would seem to the habits of the young animal 

 thus sustained, while they depend in part upon the nature of 

 the food supplied to the animal that forms the milk ; but the 

 three substances are thus combined in every instance. 



159. But although the greater part of the organised tis- 

 sues of animals have a composition nearly allied to that of 

 albumen, many of them also contain a large quantity of 

 gelatin ( 19). It seems certain that this gelatin may be pro- 

 duced out of albuminous substances ; since in animals chat 

 are supported on these alone, the nutrition of the gelatinous 

 tissues does not seem to be impaired. But it appears equally 

 certain, that gelatin cannot be applied to the nutrition of the 

 albuminous tissues. Many series of experiments have been 

 made on this subject, with a view of determining how far 

 gelatin-soup made from crushed bones (such as that which 

 long constituted a principal article of diet in the hospitals of 

 Paris) is adequate for the support of the body in health. 

 The result of these has been uniformly the same, namely, 

 that although gelatin may be advantageously mixed with 

 albumen, fibrin, gluten, &c., and those other ingredients which 

 exist in meat-soup and bread, yet that, when taken alone, it 

 has little (if any) more power of sustaining life, than sugar 

 or starch possesses. Although it might have been thought 

 likely that gelatin employed as food might be applied within 

 the body to the nutrition of its gelatinous tissues, yet there 



