104 OF FOOD, AND THE DIGESTIVE PROCESS. 



that a definite line could be drawn between the non-azotized, including the 

 oleaginous and saccharine substances, on the one hand, and the azotized, 

 embracing the albuminous group and gelatin, on the other; the former being 

 subservient to the production of heat, the latter to the repair and develop- 

 ment of the different tissues. To a certain extent this division is unques- 

 tionably based on correct principles. The presence of a large proportion of 

 Nitrogen in all the higher tissues of the Animal body clearly indicates that 

 for their due nutrition some substance containing Nitrogen should be con- 

 sumed as food; and the justice of this inference has been fully borne out by 

 experiment. In this sense, then, the albuminous and gelatinous substances 

 are truly histogenetic. On the other hand, the large proportion of Carbon 

 and Hydrogen in saccharine and oleaginous compounds naturally suggests 

 that the chief purpose to which they are applied in the body is the mainte- 

 nance of its temperature by their combination with oxygen. But the mus- 

 cular, nervous, and glandular tissues are not composed of albuminous sub- 

 stances alone ; they contain, as an essential constituent of their structure, a 

 certain portion of fat, without which their composition would be imperfect, 

 and the performance of their functions impossible. Such fat, then, must be 

 considered as "histogeuetic" and not as "calorifacient" fat; though like 

 that which exists in the free state in the blood, or is stored up in the adipose 

 tissue, after having fulfilled its functions, it may be applied by its combus- 

 tion to the support of the animal heat and the production of nervo-muscular 

 force. In a manner essentially similar, the albuminous substances ingested, 

 whilst partly becoming assimilated and applied to the nutrition of the tissues, 

 are partly also directly decomposed in the blood; the products of their dis- 

 integration in both instances combining with oxygen, and yielding a certain 

 amount of heat or other force; so that, like the oleaginous and saccharine 

 substances, they are applied to the carrying out of both provisions, the form- 

 ation of tissues, capable of generating uervo-muscular, or other form of ac- 

 tivity, and the maintenance of an elevated temperature, though undoubtedly 

 in each case to a very unequal degree. It is, however, impossible to measure 

 the value of any particular kind of food for either purpose by a consideration 

 merely of its ultimate or even of its proximate constitution; since its fitness 

 as an article of diet will also depend upon the facility with which it may be 

 reduced by the digestive process, and afterwards assimilated. Thus an ali- 

 ment abounding in nutritive matter, may be inferior to one which really 

 contains a much smaller proportion, if only a part in the first case, and the 

 whole in the second, be readily taken up by the system. 



63. It is obvious that the most economical diet will be that in which there 

 is the most perfect apportionment of the several classes of constituents to the 

 wants of the system; and these will vary with the amount of muscular ex- 

 ertion put forth, and with the elevation or depression of the external tem- 

 perature. Thus, for a man of ordinary habits, and living under a medium 

 temperature, a diet composed of either bread or of animal flesh alone is far 

 from being the most economical. No doubt there are particular conditions 

 of existence, under which life may be advantageously supported upon iiniiiutl 

 fond alone. Thus the Guachos of South America, who pass the whole day 

 in the saddle, and lead a life of constant activity resembling that of a car- 

 nivorous animal, scarcely ever taste anything but beef; and of this their 

 consumption is by no means great; for the temperature of the surrounding 

 atmosphere is so high, that the body has no occasion to generate more heat 

 than is supplied by the combustion of the hydrocarbonaceous portion of the 

 albumen of the food or of "waste" of the tissues. Here, then, the demand 

 for histogenetic material being at its maximum, and that for combustive 

 materials at its minimum, the former supplies all that is requisite for the 



