05 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



litmus paper, but perhaps more strikingly by the use of acid fuchsin.* 

 If a solution of acid fuchsin is injected under the skin of a frog it 

 is gradually absorbed and distributed to the body without injuring 

 the tissues. In the normal media of the body this solution remains 

 colorless or nearly so. If now one of the legs is tetanized the 

 muscles 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 act- 

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

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

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

 animal by the fact that the acid is removed by oxidation or by 

 the circulating blood. This conclusion has been confirmed in a 

 satisfactory way by the striking experiments of Fletcher and 

 Hopkins.f These observers have shown in the first place that 

 injury to a muscle causes a production of lactic acid, and that, 

 therefore, the usual method of determining the amount of this 

 substance in supposedly resting muscle has given fallacious 

 results owing to the injury inflicted during the process of extrac- 

 tion. By the adoption of a new method they have avoided this 

 error, and they find that in resting muscle lactic acid exists in 

 traces only (0.03 per cent.) or perhaps is absent altogether. 

 An appreciable amount is formed when the excised muscle is 

 well tetanized (0.22 per cent.), also after injury, and especially 

 in the development of rigor. In heat-rigor a maximum yield 

 of 0.3 to 0.5 per cent, is obtained in the frog's muscle. In a 

 muscle removed from the body and deprived, therefore, of its 

 supply of oxygen, lactic acid develops rapidly, reaching finally 

 an amount equal to that observed in heat-rigor. As long as 

 such a surviving muscle shows irritability toward artificial stim- 

 ulation, lactic acid continues to form. When irritability is lost, 

 no further production of acid can be detected and the muscle 

 soon goes into death-rigor. On the contrary, if the muscle is 

 supplied abundantly with oxygen, no accumulation of lactic acid 

 can be detected. It is evident from these observations that 

 lactic acid is formed in the muscle as a result of the chemical 

 changes underlying contraction, and also of the changes that 

 occur during dying. The interpretation of this fact and also 



* Dreser, "Centralblatt fur Physiologic," 1, 195, 1887. 



f Fletcher and Hopkins, "Journal of Physiology," 1907, 35, 247; also 

 1911, 12, 43, 286, and Embden, et. al., "Bioehemiaehe Zeitschrift," 1912, 45, 

 45. 



