717 



time of the muscle. In every animal "the swiffer the action of the 

 muscle, the gj-eater the rate of propagation of the impulse in the 

 motor nerve suppl^'ing the muscle". All the nerves are, so to say, 

 tuned to the muscle thej supply. 



This relation having been established, Lapicque and Lkgendre ') 

 examined which anatomic characteristic of the nerve libers answers 

 to those physiological properties. They found for the common Frog 

 (Rana esculenta) that the thickness of the nerve fibers regularly 

 increases with the rate of conduction of the influxion, to be measured 

 by the rapidity of contraction in the muscle. It may be derived from 

 the values communicated by them that the rapidity in question in 

 the nerve fiber varies in geometrical ratio with the area of the 

 section of the nerve fiber. They also found with regard to the Rabbit, 

 that among others the nerve fibers for the rapid adductor magnus 

 muscle are thicker than those for the semitendinosus, which is a slow 

 muscle. These data make it highly probable that the principle holds 

 good universally : "Les fibres nerveuses sont d'autant plus rapides 

 qu'elles sont plus grosses." 



Lapicque demonstrated further that the movements of different 

 Amphibians are the quicker or the slower as the rate of propa- 

 gation of influxions in the nerves of the hind-legs is greater or 

 smaller. *) For the slow Common Toad (Bufo vulgaris) the rate of 

 conduction in the nerve for the musculus gastrocnemius is onlj 

 about half so great as for the common Frog (Rana esculenta), which 

 jumps quickly and far. The Frog-toad (Pelobates fuscus), far exceeds 

 the Toads proper in the rapidity of its movements, and has, in 

 agreement with this, equally rapid nerves in its hind-legs as the Frog. 

 But also the Green Toad (Bufo viridis), which is more agile and 

 quicker than the Common Toad, which makes comparatively big jumps, 

 and swims and climbs well, is on a par with the Frog as far as 

 the rate of conduction in the nerves is concerned. Though the 

 Walking Toad (Bufo calamita) does not, indeed, jump like the Frog, 

 it runs almost as fast as a mouse (hence its other name cursor), 

 it swims nimbly and rapidly, climbs better than any other Toad 



1) L. Lapicque et R. Legendre, Relation entre Ie diamètre des fibres nerveuses 

 et leur rapidité fonctionnelle. Gompies rendus de l'Académie des Sciences. Paris 

 1913 (2). Tome 157, p. 1163—1166. Also: La rapidité fonctionnelle des fibres 

 nerveuses mesurée par la chronaxie et son substratum anatomique. Bulletin du 

 Muséum d'histoire naturelle. Année 1914, W. 4, Paris 1914, p. 248 — 25i2. 



2) Louis Lapicque, Rapidité nerveuse des membres postérieurs chez divers 

 Batraciens anoures. Bulletin du Muséum d'histoire naturelle, Année 1914. N^. 6, 

 p. 363—366. 



