464 METABOLISM IN MUSCLE. 



however, the glycogen of muscle does not pass into lactic acid, as during rigor 

 mortis, if putrefaction be prevented, the amount of glycogen does not diminish. 

 If muscle be suddenly boiled or treated with strong alcohol, the ferment is destroyed, 

 aud hence the acidification of the muscular tissue is prevented (Du Bois-Reymond). 

 Acid jxttassium phosphate also contributes to the acid reaction. 3. Carnin 

 (C-HoN Oo) which is changed by bromine or nitric acid into sarkin, occurs to the 

 extent of 1 per cent, in Liebig's extract of meat ( Weidel). 4. Urea, 0*01 per cent. 

 (Haycraft). [There is much urea in the muscles of the skate.] 5. Glycogen 

 occurs to the amount of over 1 per cent, after copious flesh feeding, and to 0"5 

 per cent, during fasting. It is stored up in the muscles, as well as in the liver, 

 during digestion, but it disappears during hunger. It is perhaps formed in the 

 muscles from proteids ( 174, 2). 6. Lecithin, derived in part from the motor 

 nerve-endings ( 23 and 251). 7. The gases are C0 2 (15 to 18 vol. per cent.), 

 partly absorbed, partly chemically united ; some absorbed N, but no O, although 

 muscle continually absorbs O from the blood passing through it (L. Hermann). 

 The muscles contain a substance whose decomposition yields C0 2 . When muscles 

 are exercised, this substance is used up, so that severely fatigued muscles yield 

 less C0 2 (Stinzing). [All muscles have not the same chemical composition.] 



294. METABOLISM IN MUSCLE. [In living muscle we have to study the 

 transformations of energy, and the chemical changes on which these depend. But 

 as we cannot examine the chemical changes which occur during a contraction, we 

 are confined to a study of (1) the composition of a muscle before and after contrac- 

 tion, and (2) the effect of contraction on the medium surrounding or passing through 

 a muscle. We may observe the effect produced by a muscle upon air or other 

 gases to which an excised muscle is exposed, or we may investigate the changes 

 which the blood undergoes in passing through a muscle, and if the muscle be still 

 in situ, the effect upon the general excreta. These methods may be applied to 

 muscle in various conditions, passive or active, dead or dying, to excised muscles 

 or those still under normal circumstances.] 



I. A passive muscle continually absorbs a certain amount of O from the blood 

 flowing through its capillaries, and returns a certain amount of C0 2 to the blood- 

 stream. The amount of C0 2 given off is less than corresponds to the amount of O 

 absorbed. Excised muscles freed from blood exhibit an analogous but diminished 

 gaseous exchange. As an excised muscle remains longer excitable in O or in air 

 than in an atmosphere free from O, or in indifferent gases, we must conclude that the 

 above-named gaseous exchange is connected with the normal metabolism, and is 

 a condition on which the life and activity of the muscle depend. [Resting 

 living muscles also exhale C0 2 .] 



If a living muscle be excised, and if blood be perfused through its blood-vessels, the amount 

 of O used up is, within pretty wide limits, almost independent of temperature ; if the variations 

 of temperature be great, it rises and falls with the temperature. The C0 2 given off by muscular 

 tissue (less than the used up) falls when the muscle is cooled, but it is not increased when 

 the muscle is subsequently warmed {liubner). 



This exchange of gases must be distinguished from the putrefactive phenomena due to the 

 development of living organisms in the muscle. These putrefactive phenomena are also con- 

 nected with the consumption of and the excretion of C0 2 , and occur soon after death (Z. 

 Hermann). 



II. In an active muscle the blood-vessels are always dilated (Ludwig and 

 Sczelkow, Ga&kell) a condition pointing to a more lively material exchange in the 

 organ. [The dilatation of the blood-vessels can be observed microscopically in the 

 contracting mylo-hyoid muscle of the frog.] Hence, the active muscle is distin- 

 guished from the passive one by a series of chemical transformations. 



1. Eeaction. The neutral or feebly alkaline reaction of a passive muscle (also 

 of the non-striped variety) passes into an acid reaction during the activity of the 

 muscle, owing to the formation of paralactic acid (Du Bois-Reymond, 1859) ; the 



