/ - V 'f Iff 



J -iA THE WONDERS OF LIFE 



,'l M hydrogen, and one to two per cent, sulphur. However, 

 " ' ' M there is a good deal of variety and complication in the 

 ^1 j\ way in which the atoms of these five elements are com- 

 ^r bined in albumin and their molecules are grouped. 



Hence the question of the chemical nature of the 

 plasma-substances compels us now to look for a mo- 

 ment at the larger group of albuminoids to which they 

 belong. 



The carbon-compounds which we comprise under the 

 chemical title of the albumins or proteids are the most 

 remarkable, but also, unfortunately, the least known, 

 of all bodies. The attempt to examine them closely 

 encounters extraordinary difficulties, greater than in any 

 other group of chemical compounds. Everybody is 

 familiar with the appearance of ordinary albumm, from 

 the transparent viscous albumin that surrounds the yolk 

 in the hen's egg, and which becomes a white, opaque, 

 and solid mass when it is cooked. However, this special 

 form of albumin, which we can get so easily in any 

 quantity from the eggs of birds and reptiles, is only one 

 of the innumerable kinds of albumin, or species of 

 protein, that are to be found in the bodies of the various 

 animals and plants. Chemists have hitherto tried in 

 vain to master the chemical structure of these obscure 

 protein-compounds. They are only rarely to be found 

 in chemically pure form as crystals. As a rule, they are 

 in the colloid form, or uncrystallized jelly-like masses, 

 which offer a much greater resistance than cr3^stals to 

 the passage through a porous medium by diosmosis (see 

 p. 39). However, although we have not yet succeeded 

 in penetrating the molecular constitution of the al- 

 bumins, the laborious research of chemists has yielded 

 some general results which are of great importance for 

 our purpose. We have, in the first place, a general 

 idea of their molecular constitution. 



Molecules are the smallest homogeneous parts into 



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