CHAPTER V. 



OP ASSIMILATION AMONGST ANIMALS. 



> 



1. Mineral Principles. 



The mineral principles which ceaselessly introduce themselves 

 into animal organisms are, gases of the air, a large quantity of 

 water, and dissolved composite solids, of which the principal are 

 phosphate of lime, phosphate of magnesia, bi-carbonate of lime, 

 fluoride of calcium, silicious acid, chlorure of sodium, carbonate 

 of soda, alkaline phosphates, oxyde of iron, etc. Amongst the 

 lower organisms, the two chief gases of the air penetrate direct 

 through the limiting surface of the animal. Amongst others, 

 apparatus exist, varying according to species and medium, but 

 whose office is limited in final analysis to bringing the outer air 

 into contact with the black or venous blood, without other 

 barrier than a very thin organic membrane — that is to say, to 

 realizing in a special part of the organism the conditions of 

 osmotic absorption which exist over the whole surface of the 

 bodies of inferior animals. 



Of the two principal gases of the blood, the one, azote, is 

 absorbed ia smaller quantity, and seems normally to exercise no 

 function in the animal economy. It is rejected as it was 

 , absorbed, and by the same channels. Nevertheless, the animal, 

 in a state of inanition, fixes a certain portion of it in its tissues. 

 Probably there is then a direct synthesis. As a compensation, 

 when the animal enjoys an abundant azotic alimentation it 



