372 THE MUSCLE-TISSUE. 



the working muscle is constantly taking up sugar from the blood, 

 which in turn is derived from the glycogen of the liver, and that 

 its function may continue even though a deposition of glycogen, as 

 such, does not occur. This shows that the muscle glycogen, like 

 that of the liver, is in reality a reserve food, and is here deposited 

 for immediate use. In starving animals it gradually disappears, 

 but, in contradistinction to the glycogen of the liver, its supply is 

 not exhausted until the liver itself is free from glycogen. In this 

 connection it is interesting to note that the heart-muscle still has 

 glycogen at its disposal under conditions when the skeletal muscles 

 are already free from glycogen, viz., during starvation or in cases in 

 which the glycogen is rapidly consumed as the result of excessive 

 work. 



The chemical changes which are involved in the transformation of 

 glycogen into glucose are probably the same as those which occur 

 during the process of digestion. Erythrodextriri thus first results, 

 and is then transformed into achroodextrin, and this into maltose, 

 which in turn is inverted to glucose. This is then supposedly de- 

 composed through the agency of a specific muscle-ferment, activated 

 by a pancreatic kinase. Recent research has shown that this de- 

 composition must be effected with the intermediate formation of 

 acetic aldehyde and formic acid, as shown in the equation : 



C 6 H 12 6 = 2CH 3 .COH -f 2H.COOH. 



The aldehyde may then be reduced to ethyl alcohol, carbon dioxide 

 and water ultimately resulting. Lactic acid, it will be noted, is not 

 formed during this process, but may result under certain circum- 

 stances instead, from antecedents which will stand intermediary be- 

 tween glucose and acetic aldehyde and formic acid. The details of 

 the entire process, however, are very little understood. The amount 

 of carbon dioxide that is eliminated during a period of exercise, as 

 compared with one of rest, may serve as an index of the amount of 

 muscular work done. I have already pointed out that the nitrog- 

 enous constituents of the muscle-tissue cannot be regarded as a 

 source of muscular energy, and that this must be sought in its 

 non-nitrogenous components. This fact was well shown during the 

 ascent of the Faulhorn mountain by Fick and Wislicenus, in which 

 it was calculated that the total amount of work done by the latter 

 amounted to at least 368,000 kilogram meters. The amount of nitrogen 

 which he eliminated during the ascent and the six hours following 

 corresponded to 37 grammes of albumin. Translated into calories, this 

 would represent about 106,000 kilogrammeters of work. Deducting 

 this from 368,000, there would remain 262,000 kilogrammeters, 

 which could not be accounted for by a decomposition of nitrogenous 

 material, and which must hence be referable to the destruction in the 

 muscles of other bodies which are free from nitrogen. Of these, the 

 glycogen which is referable to ingested carbohydrates is no doubt the 

 most important. While normally the muscle glycogen is prob- 



