472 Prof. Liebig on the Constitution of 



substances owe iheir origin and formation to the circumstance 

 of the lactic acid sharing the bases with the phosphoric acid. 



" In the course of an investigation into the constitution of 

 urine, in the year 1807) I found lactic acid as a constituent of 

 urine; this acid had not, up to that period, been counted 

 among the constituents of urine ; and several chemists having, 

 on very slight grounds, asserted it to be acetic acid, I sub- 

 mitted it to the test of a new examination ; the results of this 

 examination led me to conclude that lactic acid could not be 

 confounded with acetic acid, and that the acid found was 

 lactic acid, and not acetic acid. 



"The lactic acid contained in the urine is the principal 

 solvent for the phosphate of lime ; this may be easily seen 

 from the fact, that after having extracted from exsiccated urine 

 the free lactic acid by means of alcohol, the residue indeed 

 contains acid phosphates, but upon redissolving it in water it 

 leaves the greatest portion of the phosphate of lime as an in- 

 sokible residue." 



I deem it scarcely necessary to examine the reasons which 

 induced Berzelius, thirty-seven years ago, to assume the pre- 

 sence of lactic acid (a substance the properties of which were 

 then totally unknown) in urine and in animal fluids. The 

 then prevailing idea that lactic acid must be a product of the 

 decomposition of all animal fluids, because it is formed in milk, 

 has now turned out to be totally unfounded. Milk contains 

 neither lactic acid nor lactates, the formation of lactic acid in 

 milk being dependent upon milk-sugar. 



It was evidently from entertaining these incorrect notions 

 that Berzelius was led to assume the presence of lactic acid in 

 certain non-volatile fluids of the urine, which have an acid 

 reaction, and contain organic substances beside phosphoric 

 acid ; there is no doubt that the presence of lactic acid in 

 these fluids was highly probable, if lactic acid were truly a 

 constant product of the putrefaction o^ all animal fluids. But 

 when we consider that the properties of lactic acid were then 

 so little known that many chemists even disputed the fact of 

 its existence, and asserted it to be nothing more than acetic 

 acid in disguise, we see clearly that there could exist no ana- 

 lytical grounds, at that time, whereon to found a positive as- 

 sertion of its presence in urine and other animal fluids. At 

 present there is far less reason for such a supposition, since 

 now we have closely examined and studied this acid, and 

 have obtained a correct knowledge of its properties, and yet 

 we are incapable of detecting even a trace of it in any animal 

 fluid. 



In the nineteenth volume of Poggendorff^s Amialen der 



