136 



HITCHCOCK'S ANATOMY 



gen is the cause of the inability to exertion experienced in the 

 thin air of mountain tops and the relaxation of the muscles in 

 fainting from exposure to carbonic acid, ether, or chloroform. 

 On the other hand, the more full the respiration, the more ener- 

 getic the muscular power. The effect of oxygen upon the tis- 

 sues is that of waste, or a consumer ; that is, it produces a more 

 rapid circulation of matter by removing the carbonic acid, 

 and substituting itself in its place ; and the deeper the respi- 

 ration, the more energetically will all the functions of the 

 body be carried on. Hence a plausible theory offers itself 

 to explain the cause of muscular contraction, which is, that 

 " muscular contraction is the necessary physical result of mus- 

 cular disintegration." 



267. The Mechanical Disadvantage at which many 

 Muscles Act — The Reason of it. — The force of muscular 

 contractions is almost always very great, sometimes so pow- 

 erful that some of the fibers are ruptured. But the main 

 evidence of this great force is exhibited in the mechanical dis- 

 advantage at which most of the muscles act. For instance, 

 Fig. 151. if the muscles were 



attached at c, a much 

 greater weight could 

 be lifted by the ex- 

 penditure of the same 

 power than if it were 

 attached at b ; but a much longer portion of time would be 

 necessary to produce contraction in such a length of fiber, a 

 c, than in a shorter portion, a b. Besides, in most cases it 

 would be quite impossible for the muscles to contract suffi- 

 ciently to effect what they now do, since muscular fiber can 

 not shorten itself more than one third of its whole length, as 

 measured when uncontracted, or in a state of rest. 



What, however, do we know about deficiency of oxygen as affecting these properties? 

 Instance ether and chloroform also. What hypothesis has been suggested owing to the 

 waste produced by oxygen ? 267. How is muscular power well illustrated? What loss 

 And what gain are both experienced by this construction ? 



