448 THIRD CLASS OF MINERAL CONSTITUENTS. 



It is worthy of remark that, while plants, and especially the 

 grasses, contain almost all their magnesia in combination with 

 phosphoric acid, the urine of herbivorous animals so frequently 

 contains carbonate of magnesia. We can hardly suppose that 

 the phosphate of magnesia in the animal body is robbed of its 

 electro-negative constituent by a de-oxidation of the phosphoric 

 acid, which is replaced by the weaker carbonic acid ; it is much 

 more probable that the combinations of lime with vegetable acids, 

 conveyed into the animal body with the vegetable food, undergo 

 such a decomposition with the phosphate of magnesia either in the 

 blood or in other parts, that bone-earth and a vegetable salt of 

 magnesia are formed, the latter being subsequently converted into 

 carbonate of magnesia. The fact that the urine of herbivorous 

 animals is poor in phosphates seems to confirm this view. 



The egg-shell of birds contains not only carbonate of lime, but 

 also carbonate of magnesia ; both these salts are in part derived 

 from the embryo during the incubation of the egg. (Prout* and 

 Lassaignef.) 



MANGANESE. 



Minute quantities of this metal exist in the animal organism 

 as elsewhere, in association with iron : manganese, however, seems 

 to differ from iron in being devoid of influence on the metamor- 

 phosis of the animal tissues, for it appears in comparatively larger 

 quantities in the excretions than in any of the fluids that take part 

 in the vital functions. Like other heavy metals incidentally occur- 

 ring in the organism, it is principally separated by the liver ; hence 

 it is found in comparatively large quantity in the bile. 



Manganese has been found by VauquelinJ in the hair, and by 

 Bley, Wurzer||, and Bucholz^f, in gall-stones and urinary calculi. 

 Weidenbusch found 0'12 of proto-sesquioxide of manganese, and 

 0'23 of peroxide of iron in the ash of the bile, analysed by Rose's 

 method. 



* Philosophical Transactions for 1822, p. 381, 



t Journ. de Cliim. med. T. 10, p. 1U3. 



J Ann. de Chim, T. 58, p. 41. 



Op. cit. 



II Op. cit. 



1f Op. cit. 



