130 



IRRITABILITY 



Fig. 20. 



Curves of muscle contraction obtained by stimulation of 3 and 4 points situated 

 at equal distances from eacti other on tlie sciatic nerve of tlie frog. The 

 increase of length of the nerve stretch corresponds with an equal increase of 

 the latent period of contraction. From tliis follovt's, that the rapidity of the 

 wave of excitation is the same at all points of the entire length of the nerve. 

 (After Engelmann.) 



between the types of conduction of excitation in the rhizopods 

 and in the nerve. Whereas in the rhizopods the rapidity of con- 

 duction is dependent upon the intensity of the stimulus, it has 

 been long known as the result of investigation by Rosenthal, 

 Briicke and Lautenbach and at a more recent date by Gotch^ and 

 Piper, ^ that in the nerve of the frog, as well as in man, the velocity 

 is not dependent upon the intensity of stimulation. (Figure 21.) 

 Contrary results have been obtained by a few early observers 

 wherein the latent period was shorter when the stimulation was 

 strong. Nicolai^ explains this shortening of the latent period, 



1 Gotch: "The submaximal electric response of nerve to a single stimulus." Journal 

 of Physiology, Vol. XXVIII, 1902. 



2 Piper: Ueber die Leitungsgeschwindigkeit in den markhaltigen menschlichen 

 Nerven. Pflugers Arch. Bd. 124, 1908, und Bd. 127, 1909. 



3 Nicolai: "Ueber Ungleichformigkeiten in der Fortpflanzungsgeschwindigkeit des 

 Nervenprincips, nach Untersuchungen am marklosen Riechnerven des Hechts." Arch, 

 f. Physiologie 1905. 



