. VII. ELEMENTS OF RESPIRATION. 145 



the space of one day, 2465 grammes of carbon in the state 

 of carbonic acid. It is very clear, then, that the carbon of 

 the azotised principles of the aliments is only a small por- 

 tion of that which is found in the carbonic acid expired. 



Necessity for the Elements of Respiration. Hence arises 

 the necessity of other kinds of foods, to supply the deficiency 

 of carbon of the azotised aliments. Starch, gum, or sugar, 

 and the fatty bodies, come under this category. In all 

 cases where the animal economy is destined to grow, as in 

 the young animal, nature has augmented, in its foods, the 

 proportion of those ingredients which furnish the carbon 

 and hydrogen lost by respiration ; and in this way the azo- 

 tised aliments, destined for the growth of the tissues, are 

 economised. 



By successively ascertaining the weight of the fatty mat- 

 ters, and the azotised neutral matters in the egg of the 

 chick, during the period of incubation, and in the chick 

 itself after its escape from the egg, Dr. Cappenzuoli has re- 

 cently discovered, that about the seventeenth day, that is 

 to say, a short time before the chick is hatched, there is a 

 sensible diminution of the fatty and azotised neutral matters, 

 and that this diminution gradually augments. 



With respect to the fatty bodies, it seems that these are 

 exclusively employed in respiration, in those cases only 

 where the starch, sugar, and gum are insufficient. Hence, 

 the fat disappears in hybernating animals, and in those 

 which remain a long time without food. These bodies 

 appear to be, physiologically, destined for the formation of 

 the cerebral and nervous substance, and to fill the interstices 

 of the cellular tissue, where are kept in store the materials 

 for respiration.* 



* Fatty matter appears also to be intimately concerned in growth and 

 nutrition, healthy and diseased. See some interesting remarks on this 

 subject by Mr. Gulliver, in The Works of Hewson, p. 88, ^published by the 

 Sydenham Society. J. P. 



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