On the existence of Lactic Acid in Living Bodies. 129 



digested with carbonate of lead, till it contained oxide oflead 

 in solution. After having separated the sulphate and chloride 

 oflead by filtration, the fluid was treated with sulphuretted 

 hydrogen and evaporated : it was strongly acid, but yellow. 

 Supposing it might contain foreign matters, it was again treated 

 with water and digested with oxide oflead, which swelled and 

 produced a bulky basic salt. After this the acid was again 

 evaporated. It deposited no crystals, but remained in the 

 form of an acid syrup, which I did not succeed in rendering 

 colourless. I prepared some salts, and found that it produced, 

 with lime and magnesia, granular crystalline masses. To 

 satisfy myself as to the nature of the acid which I had obtained, 

 I compared it with other acids known at this period ; and I 

 found that it most strongly resembled the acid found by 

 Scheele in sour milk, and this 1 prepared on the occasion. I 

 convinced myself of their perfect identity, and that the latter 

 could not be better prepared in a state of perfect purity than 

 that from flesh. I then asserted that the acid was lactic acid, 

 precisely as M. Liebig now asserts, forty years afterwards. It 

 appeared evident to me that lactic acid in the animal body 

 ought to be considered as a product resulting from the use 

 of the elements of flesh, — a product which circulated in the 

 system, and which consequently would be found in the blood, 

 and be finally evacuated with the urine. In my analysis of 

 blood, which I undertook immediately afterwards, I also dis- 

 covered the presence of lactic acid by an analogous process ; 

 but as the quantity which is found in it is but very small, I had 

 some difficulty at first in acquiring complete certainty of its 

 identity. The successive analyses which I performed, by de- 

 grees, of fresh milk, urine, tears, saliva, bile, &c, all furnished 

 me with lactic acid: the alkaline fluids in minute quantity, the 

 acid ones, such as urine, milk and sweat, in larger quantity. 



Confidence was generally placed in my statements, until 

 L. Gmelin and Tiedemann in 1826, in their excellent work on 

 the act of digestion, asserted that this acid was the acetic. It 

 could not have been difficult to distinguish a volatile acid 

 from an acid which is not so ; but M. Gmelin thought that 

 the acetic acid lost its volatility by combination with animal 

 matter. This property, described by this chemist, obtained 

 confidence ; and in all works which were published after this 

 date, the acid in question was generally considered as acetic 

 acid. 



This event occasioned me to undertake a new series of re- 

 searches on lactic acid, which was published in my Treatise 

 on Chemistry, vol. iv. p. 577-585 (Dresden, 1831), in which 

 I demonstrated that it was impossible to confound lactic with 



Phil. Mag. S. 3. Vol. 33. No. 220. Aug. 1848. K 



