64 



ELECTRO-PHYSIOLOGY 



CHAP. 



exhibits polygonal Cohnheim's Areee, with a central cavity filled 

 with sarcoplasm ; each muscle-column is penetrated by a central 

 canal, and uniformly bordered by sarcoplasm. Rollett employed 

 preparations of these beetles, in which the muscles that work the 

 thigh of the hind pair of legs were directly excited by induction 

 shocks. These experiments exhibited a fundamental difference 

 in form and duration of the single contraction in the two species. 

 The curve of Dytiscus rises abruptly to the maximum of contrac- 

 tion, and then sinks quickly back to the abscissa. The curve of 

 Hydrophilus reaches its maximum much later, maintains it for a 

 longer time, and then sinks gradually (the myogram of cockchafer 

 muscle is even more extended) (Fig. 36). The course of contrac- 



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Fio. 3(5. A, Contraction curve of leg-muscle of Dytiscus; II, of Hydrophilus; C, of Melolontha ; 

 traced at uniform rate of the recording surface. (Rollett.) 



tion in Dytiscus is therefore comparable with that of the pale 

 muscle, of Hydrophilus and Melolontha with that of the red 

 muscle, in rabbit. For the rest, the absolute duration of a 

 twitch and its component periods varies in every case within 

 tolerably wide limits. The following table from Rollett gives the 

 averages of a great number of single experiments : 



If this is compared with the numbers given by Marey (11) 

 as the possible rate of contraction per second in the wing-muscles 

 of different insects, the extraordinary disparity of the two kinds 

 of muscle is most clearly established : 



