434 OF NUTRITION. 



the quantity ingested, that is not thus consumed. The quantity of fatty matter 

 in the blood is liable to sudden augmentation, from the introduction of a large 

 quantity furnished at once by the alimentary material ; and this excess will 

 continue until the surplus has been eliminated, either by the combustive, the 

 nutritive, or the excretory operations. These last do not ordinarily remove 

 the saponifiable fats from the body ; for although the mammary secretion in 

 the female draws off from her blood a large quantity of fatty matter, this is 

 destined not for its purification, but for the nutrition of her offspring; and 

 cholesterin appears to be the only fatty substance which is normally excreted 

 for the purpose of being removed from the body. The ultimate disposal of 

 the saccharine constituents of the body, which appear to be partly derived from 

 without, and to be partly the result of the decomposition of the albuminous 

 constituents of the blood, as will be hereafter more fully considered (Gly- 

 cogeny), is still unknown ; though there seems to be some probability in 

 favor of their being first converted into Lactic acid, and finally into Car- 

 bonic acid and Water, and as these are more easily oxidized than the fats, 

 they spare the latter from combustion. 



345. The uses of the various Inorganic compounds, which, as being uni- 

 formly present in the Blood, must be considered among its integral constit- 

 uents, have already been pointed out ( 57), and it need only here be 

 remarked that the recent observations of Weiske 1 show that the bones retain 

 their hold of the salts that enter into their composition with great tenacity, 

 so that if food be supplied in which the proper salts are defective no material 

 difference can be detected for a considerable period in the composition of the 

 osseous tissue. Papillon 2 has demonstrated that the Bones will contain a 

 large proportion of strontium phosphate, or of magnesiau phosphate, re- 

 placing the calcium phosphate, if these salts are liberally given with the 

 food, and providing the calcium phosphate is deficient or altogether absent. 



346. We may now proceed briefly to consider what is the amount and 

 nature of the work done in and by the body, and endeavor to ascertain the 

 mode in which the food consumed is applied to the production of that work. 

 It has already been stated that the two principal circumstances occasioning 

 a demand for alimentary material are the supply of the loss caused by the 

 activity of the nervo-muscular apparatus, and the production of the heat 

 requisite to maintain the body at a uniform standard. The actual disin- 

 tegration of the material substratum of the nervous and muscular tissues 

 during exertion appears to be exceedingly small, since fasting animals, or 

 animals fed on non-nitrogenous diet, can for a considerable period perform 

 severe work without the occurrence of any considerable increase upon the 

 amount of nitrogenous excreta eliminated by the same animals when at rest 

 with the same diet. Yet that the tissues really undergo disintegration during 

 exertion, and that they require appropriate nitrogenous food for the repair 

 of the loss occasioned by their wear and tear, is clearly shown by their in- 

 capacity for performing work except for a limited period without such sup- 

 plies. It is reasonable then to suppose that whilst a certain small portion of 

 the large store of albuminous and other nutritive material present in the 

 body is applied to the nutrition and repair of the work-performing tissues, a 

 very much larger proportion is applied to the development of the forces of 

 various kinds which are exerted by them. The three principal classes of 

 food, the albuminous, farinaceous, and oleaginous, are all of them composed 

 of easily oxidizable material, and it is conceivable that in the act of com- 



1 Zeitschrift fur Biologie, vii, pp. 179 and 333. 



2 Journal de 1'Anatomie, 1873, No. 3 ; see also Konig, Zoits. f. Biologic, B. x, 

 1874, p. 68. The stutement is contested by Weiske, ibid., 1872, Bd. viii, p. 239. 



