LACTIC ACID. 99 



acid in solution contaminated merely with extractive matter. After 

 the evaporation of the alcohol the acid was filtered through animal 

 charcoal, from which the earthy salts had been separated, and 

 treated with hydrated oxide of tin, on which the comparatively 

 insoluble lactate of tin was separated. This was again decomposed 

 with sulphuretted hydrogen, and the lactic acid further examined. 

 Anselmino, Thenard, and Berzelius,* believe that they have 

 found lactic acid and lactate of ammonia in the sweat. 



Berzeliusf also conjectures that alkaline lactates exist in the 

 bile. 



In consequence of the rapidity with which the alkaline lactates 

 undergo a transformation in the blood, it would naturally follow 

 that lactic acid, when it occurs in the urine, would exist there 

 as an extremely variable constituent : and this assumption is con- 

 firmed by experience. Earnestly as I formerly maintained the 

 view that lactic acid constantly occurs in animal urine, and that the 

 acid reaction of this fluid is solely dependent on its presence, I 

 have since convinced myself that my earlier modes of analysis, 

 (when I rested satisfied with the mere exhibition of the zinc-salt) 

 though most carefully conducted, were open to deceptions in refer- 

 ence to this acid; but to maintain that the urine of healthy men 

 and animals never contains lactic acid or lactates, under any phy- 

 siological relations, is to err just as much in the opposite direction. 

 A more extended investigation has led me to the following results. 

 In all cases where the supply of lactates to the blood is very great, 

 whether this depends on an excess of acid being formed in the 

 muscles, or on the use of a diet tending to produce it, or on an 

 imperfect process of oxidation in the blood, lactic acid may be 

 detected in the urine with all the certainty which in the present 

 state of chemistry can be expected in such researches. Hence we 

 can understand why it is that, in the urine of the same individual, 

 lactic acid may on one day be present and 011 another absent; why, 

 in many persons, no lactic acid can be detected in the urine, and in 

 others again (and especially in those who in consequence of repeated 

 catarrhs suffer from partial relaxation of the pulmonary tissue, and 

 yet often think themselves perfectly well) it is constantly present 

 in the urine ; why stall-fed animals, living on amylaceous fodder, 

 excrete lactic acid by the kidneys (and in part also by the mammary 

 glands,) while under other conditions this acid cannot be discovered 



* Lehrb. d. Ch. Bd. 9, S. 393. 

 t Ibid. S. 293. 



H 2 



