172 



EXPERIMENTAL PHYSIOLOGY. 



ing adjust its writing-style under the abscissa. Shoot the 

 glass plate again, and the time curve will be recorded. 



(/.) Remove the tracing, fix it and measure it out, deter- 

 mining the length of the latent period and the duration of 

 the contraction, and of its several parts. 



3. Study the improved form of this instrument recently intro- 

 duced by du Bois, in which the glass plate is set free, and 

 the tuning-fork vibrations are recorded simultaneously when a 

 handle is pressed. It is a most elegant piece of apparatus, and 

 has a beautiful mechanism for adjusting the writing-styles for 

 the muscle and abscissa. 



4. On a Revolving Cylinder. 



(.) Arrange the drum to move at the fastest speed. 



(b.) Arrange an induction machine for single shocks, the 

 secondary circuit to be short-circuited, and arranged to 



stimulate a nerve attached 

 to a muscle placed in a 

 moist chamber, as directed 

 for the foregoing experi- 

 ments. Into the primary 

 circuit introduce besides the 

 Morse key, an electro-mag- 

 net with a marking lever 

 (Figs. 61, 66, e),and cause 

 its point to write exactly 

 under the muscle lever. 

 Arrange, with its point ex- 

 actly under the other two, 

 a Deprez' chronograph or 

 signal, in circuit with a 

 tuning-fork of known rate 

 of vibration, and driven by 

 means of abattery (Fig. 68). 



Muscular Contraction. B, battery; I he three recording levers 

 K, key in primary circuit; I., pri- are all fixed on the same 

 marv, II., secondary spiral, without stand, which should prefer- 

 a short-circuiting key ; /, muscle ably be a tangent one i.e., 

 lever ; e, electro-magnet in primary . i J i i & ,1 

 circuit; t, electric signal; & sup- ^e.rod bearing the re- 

 port ; RC, revolving cylinder. cording styles can by means 



of a handle be made to 

 rotate so as to bring the writing-styles in contact with 



