PRACTICAL PHYSIOLOGY 31 



moment when the stimulus was put into the 

 nerve, and the rise of the curve, which indicates 

 the commencement of the contraction of the mus- 

 cle, gives the period of latent stimulation. To 

 measure this period as well as the duration of the 

 contraction and relaxation of the muscle remove 

 the lever point from the smoked surface, set the 

 drum revolving at the same rate as before, and 

 allow a tuning fork of one hundred vibrations 

 per second to record its waves just below the 

 abscissa of the muscle curve, putting the bristle, 

 which is attached to the tuning fork, for a second 

 only against the drum. Cut through the paper 

 and remove it carefully from the drum. Lay it 

 on the table, and write upon it date and descrip- 

 tion. Then pass it through the varnishing trough, 

 and hang it up to dry. When dry, cut out the 

 part of the tracing which is required. 



Effect of heat and. cold on muscle contrac- 

 tion. The same nerve-muscle preparation may be 

 used, the apparatus being arranged exactly as in 

 the last experiment. Mark on a new abscissa 

 the point of stimulation. Then take the following 

 curves on this abscissa : 



1. A simple muscle curve at the room tempera- 

 ture. 



2. A simple curve after warming the muscle by 

 placing over it for two or three minutes a saddle- 

 shaped brass block which has been warmed to 

 about 30 C. Or warmed salt solution may be 

 dropped upon the muscle. 



3. A simple curve after cooling the muscle for 



