474 Prof. Liebig on the Constitution of 



tained, and shall always entertain, for my highly-honoured 

 friend whose views I am controverting, — I thus enter into a 

 searching and critical investigation respecting lactic acid, both 

 historically and analytically, it is for the interest of science, 

 and to ascertain the truth upon this highly important subject. 

 The notion of the presence of lactic acid in the animal body, 

 in the gastric juice, in the milk, in the blood, in the urine, is 

 so extensively diffused, and the part which has been assigned 

 to this acid in digestion, in the respiratory piocess, &c., is so 

 great and comprehensive, that the proof of its non-presence 

 and, consequently, of the impossibility of assigning to it any 

 share whatever in the mysterious processes of the animal or- 

 ganism, was well deserving of being supported by every ad- 

 missible reason. 



The diffusion of lactic acid, or of that acid which was as- 

 sumed to be the lactic, in the animal body, depends, moreover, 

 only upon the delusion existing, from the beginning, with re- 

 gard to this acid. Berzelius states (p. 460 of his work), when 

 alluding to Hieronymi's analysis of the urine of the lion, in 

 which that chemist asserted that he had found acetic acid, 

 " 1 have taken the liberty here to substitute the term lactic 

 acid for acetic acid, for reasons which will be apparent from the 

 preceding remarks." Now, the reason for this substitution 

 was, that Berzelius, in an experiment made for this especial 

 purpose, had found that fresh urine yields no acetic acid upon 

 distillation with a mineral acid, — a fact which, as already 

 stated, I have had occasion to confirm by my own experi- 

 ments. This substitution of lactic acid for acetic acid, where 

 the presence of the latter had been asserted previously, was, 

 in the subsequent editions of his Manual, consistently carried 

 through in all the statements of analyses of animal matter. 

 The circumstance that in milk, as well as in sour-krout, upon 

 acidification, acetic acid is invariably formed, besides lactic 

 acid, renders the propriety of this substitution the more doubt- 

 ful, since the acetic acid was thus of course wholly disre- 

 garded. 



It follows, from all we have hitherto stated, that the acid 

 nature of the urine of carnivorous animals, as well as of that 

 of man, depends upon the nature of the bases partaken of in 

 the aliments, and upon the particular form of their combina- 

 tions. In the flesh, blood, and other parts of animals, as well as 

 in the grains of the cereal and leguminous plants, there exists 

 no free alkali. The alkali which these substances contain is 

 invariably combined with phosphoric acid : the acids formed 

 in the organism by the vital process, namely, sulphuric acid, 

 hippuric acid, and uric acid, share the alkali amongst them, 



