378 



OF FOOD, AND THE DIGESTIVE PROCESS. 



with which their gelatinous constituents are absorbed and applied (by the decom- 

 position just explained) to the purpose of calorification. 1 



400. The substances which cannot be arranged under either of the preceding 

 groups, are, for the most part, of the non-azotized class; and, as they mostly 

 consist of compounds in which the hydrogen and carbon are not combined with 

 their full equivalents of oxygen, they are made to contribute to the calorifying 

 process by undergoing oxidation within the system, so as to be excreted in the 

 form of carbonic acid and water. 



401. By rules based on the foregoing data, then, we may estimate the rela- 

 tive value of different articles of food for the two distinct purposes of tissue- 

 formation and the production of heat. For the proportion of albuminous matter 

 which any substance may contain, furnishes the measure of its histogenetic 

 value; whilst the proportion of hydro-carbon uncombined with oxygen affords 

 the means of estimating its calorific power when oxidized. As in almost every 

 alimentary substance, whether vegetable or animal, the two classes of compounds 

 are mingled, the percentage of Nitrogen which it may contain affords a tolerably 

 correct measure of the amount of albuminous matter which it includes, and 

 therefore of its histogenetic value : where, on the other hand, the percentage of 

 Nitrogen is the smallest, that of Hydro-carbon is the largest, and the proportion 

 of the combustive material is the highest. The following Table 2 specifies this 

 proportion in the case of various articles used as food; Human Milk being taken 

 as the standard of comparison, and the quantity of Nitrogen it contains being 

 expressed by 100. It must be born in mind, however, that this substance is 

 intended for the nourishment of a being, that passes nearly the whole of its time 

 in a quiescent state ; and must not be supposed to be adapted for the sole main- 

 tenance of the Human body in a state of activity. In fact, it is inferior in its 

 proportion of Casein (the substance of which alone the azote forms a part) to 

 the milk of most, if not all, other Mammalia ; their young bringing their animal 

 functions into exercise at a much earlier period than does the Human infant. 



Vegetable. 



1 The common notion of the great nutritive value of soups, &c., whose supposed 

 " strength" is indicated by the firmness with which they gelatinize on cooling, is one of 

 those popular dietetic prejudices, of which it is peculiarly incumbent on the Medical Pro- 

 fession to disabuse their patients. 



2 Schlossberger and Kemp, in "Philosophical Magazine," Nov. 1845. 



