456 Prof. Liebig on the Constitution of 



urine in precisely the same manner. If either of these sub- 

 stances be mixed with water, so as to form a milky fluid, and 

 be then added to urine with an acid reaction, the acid reac- 

 tion immediately disappears, and a very considerable white 

 precipitate is formed. The fluid now manifests a feebly alka- 

 line reaction, and contains a trace of magnesia in solution. It 

 is a remarkable circumstance that magnesia withdraws the 

 phosphoric acid from the urine so completely, that a mixture 

 of perchloride of iron and acetate of potass no longer indicates 

 a trace of phosphoric acid in the urine which has thus been 

 treated with magnesia. 



Had lactic acid been the solvent of the phosphate of lime 

 and magnesia in the urine, one would have expected that a 

 corresponding amount of barytes, or of magnesia, would have 

 taken its place upon its separation. But, as I have already 

 observed, not a trace of barytes is found in solution when ba- 

 rytes has been employed for neutralizing the acid, and only a 

 slight trace of magnesia when the latter substance has been 

 used for the same purpose. 



But, as urine contains a certain amount of alkaline phos- 

 phates, i. c. phosphate of soda and phosphate of potass, and 

 as barytes and magnesia form, with phosphoric acid, insoluble 

 salts, it might have been supposed that the neutral lactates 

 formed upon the neutralization of the urine with the two bases 

 had been decomposed, together with the phosphates of soda 

 and potass contained in the urine, and transposed themselves 

 anew, with these substances, into phosphate of barytes or of 

 magnesia, and into neutral lactate of potass or soda. In this 

 case neither barytes nor magnesia could remain in solution. 

 This circumstance, therefore, renders these experiments inde- 

 cisive, and leaves the question as to the presence or absence 

 of lactic acid in urine dependent upon more direct experi- 

 ments. 



I employed putrid urine in my attempts to detect lactic acid, 

 because lactic acid is not destroyed by putrefaction, and it 

 must, therefore, of necessity, be present in putrid urine if it 

 really forms a constituent of fresh urine ; and because, if lactic 

 acid can at all he formed by the putrefaction of urine, from 

 matters containing previously no lactic acid, the question 

 whether lactic acid is to be reckoned among the constituents 

 of normal urine is at once practically decided; or, more cor- 

 rectly speaking, the problem is proved to be impossible of so- 

 lution, since we possess no means of positively determining 

 which urine may be considered of a normal constitution, and, 

 on the contrary, which is to this extent abnormal. As mat- 

 ters at present stand, therefore, with regard to this subject, it 



