CHAPTEE II. 



THE ALBUMINS. 



THE albumins, or proteins, are the most important food-stuffs 

 which animals require for their existence. Albumins enter into the 

 construction of all the tissues and organs of the body, and form the 

 groundwork of every living cell. The phenomena of life, indeed, 

 are dependent upon and centre in their presence. 



While many different forms of albumin exist, they all present 

 certain general chemical and physical characteristics which serve to 

 distinguish them as a class, and show that a close genetic relation- 

 ship exists between them. 



Elementary Composition. All albumins contain carbon, hydro- 

 gen, nitrogen, oxygen, and sulphur in certain definite proportions, 

 which vary but little in the different members of the group. The 

 variations which occur are shown in the following table : 



Carbon 50.0-55.0 per cent. 



Hydrogen 6.5- 7.3 " " 



Nitrogen 15.0-17.6 " " 



Oxygen 19.0-24.0 " " 



Sulphur 0.3- 2.4 " " 



Other elements are not found in the albumins proper, but may 

 occur in certain compound albumins, which are formed through the 

 union of an albuminous group with other more or less, complex 

 radicles. The coloring-matter of the blood thus contains iron ; the 

 most important constituents of the nuclei of cells are more or less 

 rich in phosphorus ; other bodies belonging to this order contain 

 iodine, etc. 



All albumins, moreover, contain variable amounts of mineral 

 salts, which are closely bound to the albuminous molecule. The 

 most important and constant of these are the chlorides and phos- 

 phates of the alkalies and the alkaline earths. 



Crystallization. In the eggs of certain fish and amphibia 

 so-called yolk-platelets may be observed, which apparently possess 

 a crystalline structure. Chemical examination, however, has shown 

 that these bodies do not consist of pure albumins, but also contain 

 a large percentage of lecithins and mineral salts. The so-called 

 aleuron crystals, which have been found in the seeds of certain 

 plants, are thus likewise not composed of a pure albuminous sub- 

 stance, and the same probably holds good of the little eosinophilic 

 crystalloids which may be seen in the blood of birds. Artificially 



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