98 THE LACTIC ACID GROUP. 



In exudations those, namely, after puerperal fever Scherer* 

 found both free and combined lactic acid, often in very considerable 

 quantity. (In one case there was 0'105 of free lactic acid.) In 

 the exudations in a case of empyema, he found albumen uncom- 

 bined with soda, from which he concluded that the latter had been 

 abstracted from the former in consequence of the presence of lactic 

 acid. 



Lactic acid, which was originally discovered by Scheele in milk, 

 does not occur in the healthy milk of man and animals : it is only 

 in an abnormal state, or after a strictly animal diet, that milk 

 which reddens litmus and probably contains lactic acid, is secreted. 

 It is only after exposure to the atmosphere that healthy milk 

 acquires an acid reaction, which is dependent on the formation of 

 lactic acid from the sugar of milk by fermentation. 



It is now forty-two years since Berzeliusf recognised the existence 

 of free lactic acid in the muscular fluid ; and no one who hasrepeated 

 the experiments of this most faithful and accurate experimentalist, 

 can confound this acid with any other, since its properties, and 

 those of its salts, have been made known by more recent investiga- 

 tions. Berzelius did not deem it necessary at that time to confirm 

 the proof of the presence of lactic acid in this fluid by an elemen- 

 tary analysis, although he might readily have made one. Liebig, 

 so long as he relied on the investigations of his pupils, absolutely 

 denied the existence of lactic acid in the living animal body; but on 

 instituting and publishing his own admirable inquiry respecting the 

 fluids of the muscular tissue of animals, he could no longer question 

 its presence in the muscular fluid, and even admitted its existence 

 in the gastric juice. Moreover, the free acid exists in so prepon- 

 derating a quantity in the muscles, that Liebig is of opinion that it 

 is more than sufficient to saturate the alkali of all the alkaline fluids 

 of the animal body. Berzelius thought that he had convinced 

 himself that the amount of free lactic acid in a muscle is propor- 

 tional to the extent to which it has been previously exercised. 



Berzelius separated the lactic acid from the alcoholic extracts 

 of the animal fluids in the following manner. The alkalies having 

 been precipitated by tartaric acid, the filtered acid solution was 

 digested with carbonate of lead ; the alcoholic solution of lactate 

 of lead, having been separated from the other lead- salts by filtration, 

 was then treated with sulphuretted hydrogen, which left the lactic 



* Op. cit. 



t Lehrb. d. Cb. Bd. 9, S. 573 ; Ann. d. Ch. u. Phann. Bd. 1, S. 1 ; Jahres- 

 ber. Bd. 27, S. 585-594. 



