58 IMMEDIATE PRINCIPLES OF THE TISSUES. 



verted previously into the acid phosphate, or into the forms of phos- 

 phate of lime, of magnesia, or the ammonio-magnesian phosphate. 

 The acid phosphate of soda has hitherto been found only in the 

 urine. We have seen how it may be formed from the neutral phos- 

 phate ; the basic phosphate may also exist in the economy, and be 

 converted by the union of carbonic acid into the neutral phosphate 

 and carbonate of soda. The acidity of the urine is probably due 

 to this salt. There is no free acid in fresh urine, except the uric, 

 and this in very small quantity. The constantly changing reactions 

 of this secretion are owing to the instability of the phosphate of 

 soda. (Robin and Verdeil) 



14. The Phosphate of Potassa. (KQP0 5 .) 



This very much resembles, in all its relations, the salts just men- 

 tioned. Like the chloride of potassium, it is unfavorable to the 

 exchange of oxygen and carbonic acid, since it destroys the con- 

 sistence and elasticity of the blood-corpuscles, and, like it, is also 

 much more abundant in the muscles than in the blood. Precisely 

 the reverse is true of the phosphate of soda. In the muscles of the 

 calf it is more than four times as abundant as all the other phos- 

 phates taken together. (Robin and Verdeil?) It is derived from vege- 

 table aliments mainly. It has not been found in the urine; but, as, 

 if meeting the chloride of sodium, the phosphate of soda and the 

 chloride of potassium will be formed, it probably leaves the body 

 in the form of these two salts. 



15. Carbonate of Magnesia. (MgO10 2 .) 



This salt exists rarely in the bones and in concretions, and is 

 therefore included by Lehmann among the accidental mineral con- 

 stituents of the body. It is often quite abundant in the urine of 

 herbivorous animals. 



CLASS SECOND. 



IMMEDIATE PRINCIPLES OF ORGANIC ORIGIN, FORMED WITHIN THE 

 BODY BY DIS-ASSIMILATION. 



The principles of this class are sometimes termed "secondary 

 organic compounds." They all have a definite chemical composi- 

 tion, are formed within organized bodies, vegetable and animal, and 

 exist only in them. Being, however, formed (except the fatty prin- 



