PRACTICAL PHYSIOLOGY 



39 



viz., (a) during the rise of the first curve, (d) near 

 the top of the first curve, (c) during the decline of 

 the first curve. Take these double tracings at 

 different levels of the paper, each one on its own 

 abscissa. 



Effect of several successive stimuli ; teta- 

 nus. For studying the effect on a nerve-muscle 

 preparation of a rapid succession of stimuli a vibrat- 

 ing steel reed is used to make or break the primary 



FIG. 27. TETANUS OF MUSCLE. 



circuit of the induction coil by allowing a wire at- 

 tached to its end to dip into and out of a cup of 

 mercury. The rate of vibration of the reed de- 

 pends upon its length, which can be varied by 

 clamping it at different places ; it is marked at 

 points for producing vibrations of ten, fifteen, 

 twenty, and thirty per second (Fig. 27). The 

 secondary coil should be placed at such a distance 

 from the primary that only the break shock is 

 effective. The drum may revolve at only a mod- 

 erate speed (one revolution in four or five seconds.) 



