64 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



longed muscular activity, especially in the starving animal, the 

 supply may be exhausted entirely. In what way the glycogen is 

 consumed is not completely known. It is possible that it may 

 be burnt or oxidized as glycogen or sugar, with the production of 

 CO 2 and H 2 0, the oxidation in some way being under the control 

 of the living tissue; or it may first be split into lactic acid and 

 other products, which then undergo oxidation. It is possible, on 

 the other hand, that the glycogen, after conversion to sugar, is first 

 combined with the living proteid material before undergoing oxi- 

 dation. Attention has already been called to the fact* that the 

 rigor of muscle comes on at a much lower temperature when the 

 sugar is used up, and it has been found that supplying new sugar 

 will restore the muscle to its normal condition in this respect, a 

 fact which seems to indicate that the sugar enters into a combination 

 in the living tissue. In this process of the consumption of the gly- 

 cogen two or more enzymes are supposed to be concerned. Under 

 the influence of one, amylolyase, the glycogen is changed to sugar, 

 dextrose; while other so-called glycolytic enzymes are necessary 

 for its final destruction or oxidation. The fact that the glycogen 

 disappears as a result of the contractions does not mean necessarily 

 that this substance or the sugar into which it is converted is abso- 

 lutely necessary for the chemical changes of contraction. It is 

 stated that the muscle will continue to contract after all its glycogen 

 is used upf ; 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, perhaps 

 from its proteids, 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 

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

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

 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 alkaline media of the body this solution remains 

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



* Latimer, loc. cit. 



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



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



