CHAPTER III 



THE CHEMICAL CONSTITUENTS OF THE BODY 



As already observed at page 20 we know nothing at all concerning the 

 chemical nature of the living protoplasm. And yet from the dead body we 

 are able to isolate a number of substances derived from the living proto- 

 plasm. The most important of these are the simple and the compound pro- 

 teids. Many substances occur also as nonliving cell contents and as special- 

 ized products or as assimilative products, part of which are closely related 

 to the proteids, while part have an entirely different constitution. Here 

 belong the gelatin-forming substances, fats, carbohydrates, the enzymes, the 

 products of internal secretions ( cf . Chapter XI ) , etc. Finally there are found 

 in the body itself as well as in its secretions and its excretions, numerous 

 substances which owe their origin to the dissimilative processes of the body. 

 These latter substances, as well as the enzymes and the products of the in- 

 ternal secretions, will be discussed later in connection with the physiological 

 processes involved, but it will be appropriate to treat here the products of the 

 assimilative activity of the cells, and the final decomposition products of pro- 

 toplasm so far as they are yet known to us. 



1. THE NITROGENOUS SUBSTANCES 



A. THE SIMPLE PROTEIDS 



In the purest state obtainable proteids are colloidal, slightly or not at all 

 diffusible, laevo-rotatory bodies of high molecular weight, without smell, with- 

 out taste, and as a rule amorphous. In the dry condition they are either 

 white or yellowish powders, or are made up of solid yellowish disks trans- 

 parent in thin layers. Crystallized proteid has been obtained from plant seeds 

 and from egg albumin (Hofmeister), from whey (Wichmann), and from 

 serum albumin (Griiber) (Fig. 38). 



Proteids exhibit great differences with respect to their solubility: some 

 are soluble in water, others in solutions of neutral salts, others again in weak 

 alkaline or weak acid solutions, and some are not soluble in any of these 

 fluids. 



The last mentioned can be dissolved, in part at least, by means of strong 

 acids or bases, but they at the same time undergo a transformation, and in- 

 stead of the original proteid substances we then have what are known as 

 modified proteids. 

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