60 



ELECTRO-PHYSIOLOGY 



CHAP. 



the wing-muscles of many insects the duration of a contraction 

 falls to -g-^-g- sec., lasting, on the other hand, for several 

 seconds in smooth muscle. Hand in hand with these differences 

 in the period of contraction are other differences in the size of 

 the mechanical latent period, which, as a rule, increases with in- 

 creasing duration of contraction. 



The fact that the striated muscles of the same animal may 

 present very important functional as well as histological and 

 chemical differences, is very interesting. Eanvier (5) was the first 

 to observe that the contraction period differed in the pale and red 

 muscles of the rabbit, the red being distinguished from the pale 

 muscles by a comparatively long contraction period, and a corre- 



Soleus roth (Kamnchenj 



Gastr it Led. wciss (Kaninchm) 



FIG. 34. n, Three maximal contractions loaded at 50, 100, and 200 grs.; b, four maximal 

 contractions at 50 to 500 grs. (Casli.) 



spondingly longer mechanical latent period ; the pale muscles 

 contract much more quickly after a short latent period. In par- 

 ticular, Eanvier compared the function of the red semitendinosus 

 muscle with that of the pale vastus internus, or adductor 

 magnus, in rabbit, and found on stimulating with single induc- 

 tion shocks that it did not contract quickly like the pale muscle, 

 but shortened gradually, the latent period being four times 

 greater. Kronecker and Stirling (6) confirmed these facts, finding 

 the contraction period of red muscle nearly three times as long 

 as that of the pale, while the height of contraction of the former was 

 quite insignificant as compared with the pale muscle (Fig. 34, a, l>). 

 Marey had made similar observations on the different muscles of 

 the frog, finding, e.g., that M. hyoglossus was more sluggish than 

 gastrocnemius. Cash (7) ascertained by conclusive experiments 



