METABOLISM IN MUSCLE. 465 



degree of acidity increases up to a certain extent, according to the amount of work 

 performed by the muscle (R. Heidenhain). The acidification is due, according to 

 Weyl and Zeitler, to the phosphoric acid produced by the decomposition of lecithin 

 and (? nuclein). 



It is doubtful if the acidity is due to lactic acid, as Warren and Astaschewsky find that 

 there is less lactic acid in the active than in the passive muscle. Marcuse, however, supports 

 the lactic acid theory, while Moleschott and Battistini, agree that the passive muscle contains 

 acid, but the fatigued muscle contains more, especially of phosphoric acid and C0 2 . 



2. Production of C0 2 . An active muscle excretes considerably more C0 2 than 

 a passive one : (a) active muscular exertion on the part of a man or of animals 

 increases the amount of C0 2 given off by the lungs ( 127) ; (b) venous blood flow- 

 ing from a tetanised muscle of a limb contains more C0 2 , more C0 2 being formed 

 than corresponds to the O, which has simultaneously been absorbed (Ludivig and 

 Sczelkow). The same result is obtained when blood is passed through an excised 

 muscle artificially ; (c) an excised muscle caused to contract excretes more C0 2 . 

 (Compare 368.) 



3. Consumption of Oxygen. An active muscle uses up more O (a) when 

 more muscular work is done, the body absorbs much more O ( 217) even 4 to 5 

 times as much {Regnault and Reisei) ; (b) venous blood flowing from an active 

 muscle of a limb contains less O (Ludwig, Sczelkow, and Al. Schmidt). Neverthe- 

 less, the increase of used up by the active muscle is not so great as the amount 

 of C0 2 given off (v. Pettenkofer and v. Voit). The increase of O used up may be 

 ascertained even during the period of rest directly following the period of activity, 

 and the same is the case with the C0 2 excreted (v. Frey). 



As yet, it is not possible to prove by gasometric methods, that O is used up in 

 an excised muscle free from blood. Indeed, the presence of O does not seem to 

 be absolutely necessary for the activity of muscle during short periods, as an 

 excised muscle may continue to contract in a vacuum, or in a mixture of gases 

 free from O, and no O can be obtained from muscular tissue (L. Hermann). A 

 frog's muscles rob easily reducible substances of their O ; they discharge the colour 

 of a solution of indigo ; muscles which have rested for a time, acting less 

 energetically than those which have been kept in a state of continued activity 

 (Griitzner, Gscheidlen). 



4. Glycogen. The amount of glycogen (0*43 per cent, in the muscles of a frog 

 or rabbit) and grape-sugar is diminished in an active muscle (0. Nasse, Weiss), but 

 muscles devoid of glycogen do not lose their excitability and contractility. Hence, 

 glycogen is certainly not the direct source of the energy in an active muscle. 

 Perhaps it is to be sought for in an as yet unknown decomposition-product of 

 glycogen (Luchsinger). [There is more glycogen in the red than in the pale 

 muscles of a rabbit.] 



5. Extractives. An active muscle contains less extractive substances soluble in 

 water, but more extractives soluble in alcohol (v. Helmholtz, 1845); it also 

 contains less of the substances which form C0 2 (Ranke) ; less fatty acids 

 (Sczelkoiv) ; less kreatin and kreatinin (v. Voit). 



6. During contraction, the amount of water in the muscular tissue increases, 

 while that of the blood is correspondingly diminished (J. Ranke). The solid 

 substances of the blood are increased, while they (albumin) are diminished in the 

 lymph (Fano). 



7. Urea. The amount of urea excreted from the body is not materially 

 increased during muscular exertion (v. Voit, Fick and Wislicenus). According to 

 Parkes, however, although the excretion of urea is not increased immediately, yet 

 after 1 to 1J day there is a slight increase. The amount of work done cannot be 

 determined from the amount of albumin which is changed into urea. 



[Eelation of Muscular Work to Urea. Ed. Smith, Parkes, and others have made numerous 



2 G 



