650 



- mitted to the organs of digestion being, properly 

 speaking, nutritive. The earth of the Otomacs, 

 composed of alumen and silex, furnishes proba- 

 bly nothing, or almost nothing, to the composi- 

 tion of the organs of man. These organs con- 

 tain lime and magnesia in the bones, in the 

 lymph of the thoracic duct, in the colouring 

 matter of the blood, and in white hairs ; they 

 afford very small quantities of silex in black 

 hair ; and, according to Mr. Vauquelin, but a 

 few atoms of alumin in the bones, though this is 

 contained abundantly in the greater part of 

 those vegetable matters, which form part of our 

 nourishment. It is not the same with man as 

 with animated beings placed lower in the scale 

 of organization. In the former, assimilation is 

 exerted only on those substances, that enter 

 essentially into the composition of the bones, 

 the muscles, and the medullary matter of the 

 nerves and the brain. Plants, on the contrary, 

 draw from the soil the salts that are found acci- 

 dentally mixed in it; and their fibrous texture 

 varies according to the nature of the earths, that 

 predominate in the spots which they inhabit. 

 An object well worthy of research, and which 

 has long fixed my attention*, is the small num- 

 ber of simple substances (earthy and metallic), 



* Aphor. ex Physiologia chimica Plantarum, in my Flora Freib. 

 subterraneu, p. 42. 



