270 PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 



Let US take the muscle of .a frog, apply it to tbe myrograpli, and ex- 

 cite contraction in it by means of electricity. The form of this con- 

 traction varies in the following manner, under the influence of different 

 kinds of resistance opposed to the action of the muscle : If a weight 

 be suspended to the muscle it gives the tracing «, Fig. 21. If it en- 

 counter an absolute obstacle to all further diminution of length, after 

 a few instants of contraction it gives tbe trace l>. Finally, if it eucouu 

 ters an elastic obstacle, as a rubber thread, whi(;li i^resents a surmount 

 able resistance, the muscle gives the curve c. It seems as if these dif 

 ferent forms were sufldcient to characterize the nature of the resistance 

 that the contraction of the muscle has had to overcome. 



In the first case it is the inertia of a body ; now this body, submitted 

 to the muscular force during a limited period, sliould have an acceler- 

 ated motion at first and then a diminishing motion. This is precisely 

 what the form of the curve a indicates. In the second case it is not 

 necessary to explain how the horizontal line which forms the summit of 

 the curve &, expresses the cessation of all contraction in the presence of 

 an absolute obstacle. Lastly, in the curve c, the presence of an obstacle 

 is betrayed by a deflection of the curve ; that is, by a change in the 

 rapidity of the motion which produces it ; but the contraction does not 

 cease because the obstacle is not insurmountable, but it becomes slower 

 on account of the greater resistance presented. 



I have been able to convince myself that in the above-mentioned 

 experiments the swelling of the muscle presents the same phases as its 

 change of length. In fact, I have transmitted to the myograph the mo- 

 tion produced by the swelling of the muscle, and have obtained tracings 

 xdeutical with the preceding. Finally, wishing to know if the appara- 

 tus which I have used would faithfully transmit the different phases of 

 the swelling of muscle, I made the following experiment : I applied 

 the little drum which had served to obtain the tracings from the 

 birds (Fig. 18) to my own biceps muscle, fixing it exactly in place by 

 means of a bandage, and put it in communication with the registering 

 apparatus. I then made sudden voluntary motions, as similar as I could 

 make them to each other, but applied to overcome various forms of re- 

 sistance. In one case I lifted a weight ; in another my hand was abso- 

 lutely arrested in upward motion by being placed beneath a heavy 

 table ; in still another I tied my hand to a fixed object with a rubber 

 baud which, by a short flexure of my fore-arm, req aired the utmost 

 efforts of the muscle to stretch it. 



Now the tracings Tig. 21. 



which express the] 

 swelling of the bi- 

 ceps in these three] 

 experiments repro- 

 duce the three types | 

 re])resented in Fig. 

 21, and show very 

 clearly that volun- 

 tary exertions had I 

 been subjected to I 

 different forms of resistance. I tried to force upon the muscles iden- 

 tical motions in each case, which was always a short, vigorous flexure, 

 but the nature of the resistance modified these muscular actions which 

 Avere intended to be similar to each other, and imparted to them the vari- 

 ous phases and durations which are exhibited in the figure. This being 

 settled, let us return to the muscular tracing of the great pectoral of 



