138 MANUAL OF HISTOLOGY. 



cially in view of the discrepancy of the observations made 



with it. 



Each fibre is, moreover, divided longitudinally into a vary- 

 ing number of what are called muscle-columns, held together 

 probably by a delicate cement. Between these are lodged the 

 muscle-corpuscles in the lower forms of animals. In opposition 

 to most authorities, the writer is inclined to question the exist- 

 ence of fibrillse in the living muscle, at all events, as essential 

 parts of its structure. The granular appearance of cross sec- 

 tions is in accord with the views given above, and does not 

 necessarily imply the presence of fibrillse. 



Peculiarities of voluntary muscles of different functions. 

 Ranvier was the first to discover a physiological and struc- 

 tural difference in the red and white muscles of the rabbit' s 

 leg and in some other animals where both kinds exist. He 

 found that the semitendinosus of the rabbit, a red muscle, if 

 acted on by an induction current, gradually contracted till it 

 became tetanized, and remained so until the current was 

 stopped, when it gradually relaxed. White muscles, on the 

 other hand, when treated in the same way, contracted sud- 

 denly, and continued to give jerks corresponding to the inter- 

 ruptions of the current as long as it was continued. With its 

 cessation the muscle instantly returned to its original length. 

 From this he concludes that the white muscles are those of 

 sudden action, while the red ones serve to regulate power and 

 to maintain equilibrium. As to structure, he found out that 

 the white muscles had a very distinct transverse striation, and 

 a very faint longitudinal one, while in the red the longitudinal 

 lines were very marked, interrupting the cross ones at many 

 points, and giving the fibre a granular appearance. The nu- 

 clei were much more numerous in the red fibres, and, instead 

 of being flattened and situated just beneath the sarcolemma, as 

 in the white, were oval and projected into the fibre, some even 

 lying in its interior. 



Ranvier showed later that the vascular supply of the red 

 muscles differed from the usual arrangement, which consists 

 simply in elongated meshes of capillaries in the main parallel 

 with the fibres. In red muscle, not only were the minute ves- 

 sels more numerous, but the longitudinal capillaries were more 

 varicose, the meshes nearly as broad as long, and the transverse 

 vessels, both of the capillaries and small veins, presented fusi- 



