128 BIOLOGY. [Book ir. 



is water wHcli fumislies to the immediate principles the fluid 

 medium, indispensable to nutritive exchanges, which maintains in 

 the tissues the same principles in a state of solution and emulsion, 

 in a word, of needful molecular division, so that the chemical 

 reactions indispensable to life may be accomplished. Deprived 

 of their water, living substances lose their mobility and their 

 instability, and become in a measure mineral. We know that 

 certain infusoria, rotiferous, tardigrade, and anguillule, lose or 

 recover their physiological functions according as they are dried 

 or moistened.! 



Water issues from the economy in various ways. It is 

 exhaled through the external cutaneous or mucous surfaces 

 directly in contact with the exterior medium, either in the 

 state of vapour or in a liquid state. But, amongst complex 

 animals, it is especially through certain secretory or excretory 

 organs, particularly through the renal and sudorific glands, that 

 the water of the organisms escapes and returns to the mineral 

 kingdom. 



A quantity qf mineral salts, oxydes, etc., penetrates into the 

 economy either with the water, or with the aliments, whatever 

 they may be. The principal are phosphates of lime, of magnesia, 

 of soda, of potash, sulphates and carbonates of lime, of silica, 

 of chloride of sodium, alkaline carbonates, salts of iron, etc. 



Many of these salts, though insoluble in water, ai-e dissolved 

 in the blood, by means of the albuminoidal substances, the 

 carbonic acid, and other salts, which act upon them as solvents. 

 Once in the blood, they pass into the substance of the anatomical 

 elements ; thus, in the muscular flesh, we find phosphate of lime, 

 phosphate of magnesia, and tribasical phosphate of soda. The 

 alkaline carbonates are also met with in most of the solids and 

 liquids of the economy. 



Certain of these salts form themselves within the tissues by 

 the process merely of nutrition ; thus cai-bonic acid, the result 



^ J. Gavarret, NoimeUes Hxpiriences sur les Eotifires {Jourrial du Progris, 

 t. IV., p. 421 ; t. V. p. 1). 



