64 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



It is in the last step, that of oxidation, that the heat energy is given 

 off. The fact that the glycogen disappears as a result of the con- 

 tractions does not mean necessarily that this substance or the 

 sugar into which it is converted is absolutely necessary for the 

 chemical changes of contraction. It is stated that the muscle will 

 continue to contract after all its glycogen is used up * ; still it must 

 be borne in mind that the using up of the local store of glycogen 

 does not mean that all the sugar supply of the body is consumed. 

 After the most prolonged starvation the blood contains its normal 

 ;supply of sugar, and we can only suppose that this sugar comes 

 from the material of the body itself, probably from its proteins, 

 and it remains quite possible that a constant supply of sugar from 

 some source is necessary to the chemical changes that occur in 

 normal contractions. 



The Formation of Lactic Acid. The lactic acid that is present 

 in the muscle is believed to be increased in quantity by muscular 

 activity. Attention was first called to this point by du Bois- 

 Reymond, who showed that the reaction of the tetanized muscle 

 is distinctly, acid, while that of the resting muscle is neutral or 

 islightly alkaline. This fact can be demonstrated by the use of 

 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. J 

 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 the circulating 

 blood. In accordance with this view we find that the so-called 

 titration-alkalinity of the blood may be decreased after muscular 

 activity, and some observers have shown that the lactates in the 

 blood are correspondingly increased. That lactic acid is produced 

 in the living muscle is shown by experiments 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 



* Jensen, " Zeitschrift f. physiol. Chemie," 35, 525. 



fDreser, " Centralblatt fur Physiologic," 1, 195, 1887. 



JWerther, " Pfluger's Archiv," 46, 63, 1890. 



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



