SECTION I. 



PHYSIOLOGICAL CHEMISTRY. 



CHAPTER I. 

 CHEMICAL INGREDIENTS OF THE BODY. 



THE first requisite, in the study of the vital operations, is a knowl- 

 edge of the substances which make up the animal frame. It is these 

 substances which give to the organic tissues and fluids their specific 

 character ; and the manner in which they are supplied, and the changes 

 which they undergo within the body, constitute the basis of all the 

 properties which distinguish the living structure. 



If we examine any one of the fluids contained in various parts of the 

 body, such as the blood, the lymph, the bile or the saliva, we find that 

 it is made up of a number of different ingredients, mingled together in 

 certain proportions. Thus the blood contains albuminous matters and 

 water, together with calcareous or alkaline chlorides, carbonates, and 

 phosphates. In the bile there are biliary salts, coloring matters, choles- 

 terine, and mineral substances ; and the saliva is a mixed solution of 

 albuminous and saline ingredients. The proportion of these ingredi- 

 ents, in each animal fluid, is maintained by the process of nutrition at 

 about the same standard; those which are expended and lost in the vital 

 operations being replaced by others of the same kind derived from the 

 food or produced by the transformation of other materials. 

 ' There is a similar association of different ingredients in the solid parts 

 of the body. Even where the animal tissue appears most homogeneous, 

 it contains a variety of materials, and it is probable that the minutest 

 fibre or membrane in the system is made up in the same way of several 

 constituents. In the hard substance of bone, for example, there is 

 water, which may be expelled by evaporation ; lime phosphate and car- 

 bonate, which may be extracted by solvents ; a peculiar animal matter, 

 with which the calcareous salts are in union ; and various other saline 

 substances, in special proportions. The muscular tissue contains water, 

 sodium and potassium chlorides, lime phosphate, creatine, albumen, col- 

 oring matter, and myosine. It is the object of physiological chemistry 

 to isolate these different substances from each other, to study their spe- 

 cific properties, and to learn the part taken by each in the act of 

 nutrition. 



But it is very important in this investigation to determine what are 

 the real ingredients of the animal frame, and to distinguish them from 



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