334 PHYSIOLOGY OF THE INVERTEBRATA. 



as a simple line raised above the absciss whilst the cylinder 

 was at rest. In these experiments, it had been previously 

 ascertained that the cylinder had a uniform rate of rotation 

 in inscribing by the aid of the " signal Marcel-DesprSz " the 

 interruptions of an electric current produced by a tuning-fork 

 of lOO vibrations per second. It was also ascertained that the 

 contact between the two steel points always took place at the 

 same moment of the rotation of the cylinder. Fig. 67 is an 

 example of a graphic tracing obtained with Homarus. 



The nerve was excited at A. The curve CD represents the 

 curve inscribed by the muscle when the nerve was excited at 

 the point a (Fig. 66). The curve BF was obtained by exciting 

 the nerve at h (Fig. 66). The distance between the starting 

 points of the two curves represents about looth of a second. 



Fredericq and Vandevelde measured the distance of the two 

 excited points of the nerve, putting the points of the compass 

 at each pair of electrodes, with those of the wire which were 

 turned to the side of the muscle. This distance '= 56 

 millimetres. The rate of transmission was consequently 

 100 X o'56 = 5"6 metres per second. The following results 

 were obtained in these experiments : — 



A lobster (?) weighing 5 59 grammes (without blood) ; the 

 light chela being used ; and the length of the nerve was 

 59 mm. 



Experiments 



A, interval in hundredths of a second . . o.g or 6.49 m. per second. 



■D) )7 )) I, . . 0.8 ,, 6.8 „ 



C, „ „ „ . . i.o „ 5.9 „ 



D, „ „ „ . . 0.8 „ 6.8 



A lobster {$) weighing 487 grammes (without blood) ; the 

 left chela being used; and the length of the nerve was 

 56 mm. 



Experiments 



E, interval in hundredths of a second . , i.i or 5.04 m. per second. 



I'. .. » „ . . I.I „ 5.04 



G, „ „ „ . . 1.0 „ 5.60 



Hi .1 » „ . . 0.9 „ 6.i6 „ 



