THE CHEMISTRY OF MUSCLE. 65 



take on a red color, showing that an acid is produced locally. 

 The supposition generally made is that the acidity during activity 

 is due to an increased production of sarcolactic acid. Experiments 

 have been made by a number of observers to determine quantita- 

 tively the amount of lactic acid in the resting and the worked 

 muscle, respectively. Several have stated that the amount is actu- 

 ally less in the worked muscle; others have found an increase.* 

 The balance of evidence seems to show that there is actually an 

 increased production, but that this increase may be obscured in the 

 living animal by the fact that the acid is removed by the circulating 

 blood. In accordance with this view we find that the alkalinity 

 of the blood may be decreased after muscular activity. That 

 lactic acid is produced in the living muscle is shown by experi- 

 ments f in which blood was transfused for several hours through the 

 legs of a freshly killed animal. In such cases the amount of lactic 

 acid in the blood was distinctly increased. We must believe, there- 

 fore, that lactic acid is a constant product of the chemical changes 

 of nutrition going on in the muscle, and that its production is in- 

 creased by the greater chemical activity during visible contraction. 

 This lactic acid may be partly destroyed within the muscle- itself by 

 oxidation, but in part it may be carried off by the blood as a lactate 

 to be removed probably by the action of the liver. The increased 

 acidity of the muscle during activity, especially when the circulation 

 is interrupted, is referable, in the long run, to this greater produc- 

 tion of lactic acid; but as the acid after its formation probably 

 reacts with the alkaline salts present it is usually stated that the 

 actual acidity shown to litmus or other indicator is due to acid 

 salts produced by reaction with lactic acid, presumably the acid 

 phosphate of potassium (KH 2 P0 4 ). 



Much interest has been shown in the question of the origin of 

 the lactic acid. According to some observers, it arises from the 

 carbohydrates in the muscle, the glycogen or the sugar. In support 

 of this view it has been claimed that in contraction and especially 

 in rigor mortis the glycogen disappears as the lactic acid increases. 

 This relationship, however, is denied, as far as rigor mortis is con- 

 cerned, by competent observers { ; and, so far as the processes 

 during contraction are concerned, the fact that lactic acid increases 

 .as the glycogen disappears is not a very logical proof that the former 

 arises from the latter. Another suggestion is that the lactic acid 

 arises from the phosphocarnic acid described above. This com- 

 pound, when split by hydrolysis, yields lactic acid; so that if 

 we could obtain convincing proof that such a compound exists in 



* Wcrther, "Pfliiger's Archiv," 46, 63, 1890. 

 f Berlinerblau, "Archiv f. exp. Path. u. Pharm.," 23, 333, 1887. 

 t Bohm, "Pfliiger's Archiv f. d. gesammte Physiologic" 23, 44, 1880. 

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