ir CHANGE OF FORM IN MUSCLE DURING ACTIVITY 65 



House-fly . . . .330 



Humble-bee . . .240 



Bee .... 190 



Wasp . .110 



Dragon-fly . .28 



Cabbage Butterfly ... 9 



- 



Again we see that the respective properties of the muscles are 

 more or less clearly expressed in the movements of the uninjured 

 animal. 



Thus it is proved that not only the striated muscles of 

 different animals, but those of the same species also, exhibit 

 fundamental differences in regard to the time -relations of the 

 process of contraction. Griitzner's investigations show that the 

 same holds good for the fibres of the single muscle also. Just as 

 there are quick muscles and sluggish muscles, so in many, and 

 perhaps most, cases there are quick and sluggish muscle-fibres 

 in one anatomical muscle. As early as 1805, Eitter pointed 

 out a physiological difference in different groups of muscles, 

 crediting the fiexors of the frog with a lower, " conditioned, and 

 finite," the extensors with a more considerable, " unconditioned, 

 infinite " excitability. We shall have to consider these facts else- 

 where in detail ; here it is enough to say that later experiments 

 (particularly of Eollett) show that in electrical excitation of 

 the sciatic nerve the flexors are mainly excited by weak, the 

 extensors by stronger, currents. Griitzner (12) subsequently ascer- 

 tained that the flexor muscles of the frog, with direct excitation, 

 as well as indirectly from the nerve, contract much earlier, and 

 much more rapidly, than the extensors, as is most obvious 

 with normal circulation and non - fatigue of both kinds of 

 muscle. 



In the first instance, this is only a further illustration of the same 

 proposition that different muscles of the same animal may, under 

 certain conditions, exhibit a different contraction period, and, it 

 may be added, different excitability. We shall have occasion to 

 refer to yet another observation of Eanvier, according to which 

 the triceps humeri of rabbit consisting both of red (sluggish) 

 and pale (quick) fibres contracts quickly at the beginning of a 

 long excitation series like an unmixed, " pale " muscle, owing to 

 the greater excitability of the pale fibres, but later on, when 

 fatigued, sluggishly, like red muscle, because the more excitable 



F 



