CHAPTER IV. 

 ALBUMENOID SUBSTAXCES. 



THE albumenoid substances as a class occupy the first place in im- 

 portance in the living body. Their wide distribution, their 

 abundant quantity, and the part which they take in the vital operations 

 indicate a marked distinction between them and all other ingredients of 

 the organized frame. They are derived both from animal and vege- 

 table sources, and none of the nutritious juices in either kingdom is 

 without them. But in plants, as a rule, the albumenoid substances are 

 in comparatively small quantity, while in man and animals they are 

 by far the largest part of the solid constituents of the body, and with 

 the exception of water are more abundant than any other of its ingre- 

 dients. In the blood and muscles they form nearly 20 per cent, of the 

 whole mass, and in the bones and cartilages from 30 to 40 per cent. 

 Many of them have special forms of activity which distinguish them 

 from all other organic substances ; and everywhere their chemical con- 

 stitution, their physical characters, and their physiological properties 

 show them to be directly connected with the active phenomena of 

 life. 



General Characters of the Albumenoid Substances. The first im- 

 portant feature of these substances is that they contain nitrogen as one 

 of their constituent elements. This at once distinguishes them from 

 the preceding group, and gives them a different place as ingredients of 

 the food. The quantity of nitrogen present varies from about 14 to 18 

 per cent, of their weight. Most of them contain also a small quantity 

 of sulphur, and nearly all, when incinerated, leave a minute residue of 

 lime phosphate, from which they cannot be entirely freed by the usual 

 means of purification. Their average composition by weight, accord- 

 ing to the tables of Hoppe-Seyler, Wurtz, and Gorup-Besanez, is as 

 follows : 



AVERAGE COMPOSITION OF ALBUMEXOID SUBSTANCES. 



Carbon 52.8 



Hydrogen 7.1 



Nitrogen 16.6 



Oxygen 22.1 



Sulphur 1.4 



100.0 



Their exact chemical structure has not been determined with cer- 



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