428 SECOND CLASS OF MINERAL CONSTITUENTS. 



human urine ; Fleitmann* has since found it in the ash of the 

 urine, and Fourcroy and Vauquelinf > as well as de Koninck and 

 WurzerJ in urinary calculi. It need cause no wonder that silica 

 is often found in the contents of the intestines, as it is widely 

 distributed throughout the vegetable kingdom. 



That the quantity of silica occurring in the animal organism 

 essentially depends on the greater or lesser quantity of silica in the 

 food, and consequently, that the origin of this body must be prin- 

 cipally referred to vegetable food and siliceous water (and further, 

 perhaps, in the case of birds, to the sand which they swallow,) is 

 rendered sufficiently evident from the experiments of Gorup- 

 Besanez, if, indeed, any demonstration of the fact were required. 



Plants contain far more silica than was formerly supposed ; 

 in the Equisetacea, for instance, the ash often contains 97--. 

 The best method of exhibiting its presence in the seeds 

 of the grasses, is by moistening them with a little nitric 

 acid before incinerating them; in this manner, and with the 

 aid of the microscope we may, according to Schultz, recognise the 

 presence of this substance, not only in the husks but also in the 

 ovaries of many of the monocotyledons. Hence, it is obvious, that 

 we must receive silica into the system with the bread ; we can thus 

 readily understand how it was that, after the use of rye-bread, Ber- 

 zelius found l'016 in the solid excrements, and why it is that the 

 dung of the herbivora, (whose food consists of those parts of plants 

 which are richest in silica,) contains so large a quantity of this sub- 

 stance. In the dung of the cow, Zierl|| found 4'4-g-, in that of the 

 sheep, 6'0#, and in that of the horse, 4'6. Hence, large quantities 

 of silica are often found in the intestinal concretions of herbivorous 

 animals. 



SECOND CLASS or MINERAL BODIES. 



HYDROCHLORIC ACID. 



As we are convinced by the reasons given in p. 93, that lactic 

 acid is the essential free acid of the gastric juice, we need devote 



* Pogg. Ann. Bd. 76, S. 358. 

 t Syst. des Connoiss. Chim. T. 10. 

 4: Schweig. Journ. Bd. 36, S. 321. 

 Lehrb. d. Chem. Bd. 9, S. 346. 

 II Kastn. Arch. Bd. 2, S. 4?6. 



