STRIATED MUSCLE. 77 



of the muscle to the resisting skeleton, and in the case of 

 the hardening of the biceps, which we took for an example, 

 we shall find that it is not a feature of the second form, but 

 of the elongation which the muscle undergoes, and thus pre- 

 vents it from assuming that form. 



These considerations show that the name of active muscle, 

 applied to the muscle in the second form, is extremely im- 

 proper. The muscle is no more active under this form than 

 under the first, when this form is easily assumed ; and when, 

 moreover, if the muscle meets with resistance, it might then 

 be said to be passive, like a strip of india-rubber, which can- 

 not be said to be active because it shows a tendency to 

 return to that form from which it was diverted by being 

 stretched. The only activity of the muscle consists in its 

 passage from the first to the second form ; but in each of 

 these forms it is passive, because its insertions constrain it as 

 much in the former as in the latter case. 



Chemical Phenomena. We have seen that the muscle, 

 under the first form, absorbs oxygen, and gives off carbonic 

 acid ; that it is, in short, the seat of combustion, the materi- 

 als for which are furnished by the blood. The same is true 

 of the second form, with the exception that, in this case, the 

 combustion is much more active / thus, on analyzing the 

 products evolved by a muscle which has been made to pass 

 into the second form, or on examining the waste of any 

 entire organism during severe muscular labor, we find a 

 greater absorption of oxygen and evolution of carbonic 

 acid. Combustion then appears to be sufficiently active for 

 the formation of acids, so that in a muscle which is fatigued, 

 that is, which remains long in the second form, the muscular 

 fluid becomes less and less alkaline, and at length completely 

 acid : the acid thus formed is called sarcolactic acid. 



The combustion which takes place in the muscle is shown 

 immediately by the aspect of the blood which flows from it, 

 and which resembles venous blood, black blood (rich in CO 2 

 and poor in O), the resemblance being greater in proportion 

 to the energy of the muscle. Thus, when all muscular con- 

 traction ceases, as in syncope, the venosity of the blood 

 diminishes to such a degree that the blood which flows from 

 an incision made in a vein shows nearly all the distinguish- 

 ing features of arterial blood. 1 



1 Brown- Sequard, " Du Sang rouge et du Sang noir," 1858. 

 Cl. Bernard, " Liquide de 1'Organisme," 1859. 



