32 EXPERIMENTAL PHYSIOLOGY. 



imposed upon a rapid kymograph, so that after once starting 

 to record contractions, do not move the relative position of 

 the apparatus. A signal magnet is used to indicate the 

 latent period. One tuning fork record does for the whole set. 

 Using increments of ten or twenty grams, depending upon the 

 size of the muscle, increase the load until the muscle can no 

 longer lift it. Obtain a record at each increase in the load. 



Compare the latent period, contraction period and relaxation 

 period as the load increases. 



Calculate the work done in gram-millimeters at each con- 

 traction by multiplying the load by the vertical distance 

 through which the load was moved. The latter is to be deter- 

 mined by dividing the height of contraction as recorded on 

 the drum by the magnification of the lever. Now plot a curve 

 of work and load, with work as ordinate and load as abscissa.. 



What is the relation of the magnitude of the load to the work 

 accomplished? 



INFLUENCE OF VERATRINE UPON CONTRACTION. 



It is possible with certain drugs to affect one phase of the con- 

 traction in a muscle without materially modifying the other. 

 Veratrine and to some extent glycerol and nicotine produce this 

 effect. 



*Experiment 12. Prepare one gastrocnemius muscle of a frog 

 without injury to the circulation of the other gastrocnemius. 

 Inject a few drops of 0.1% veratrine acetate solution into the 

 dorsal lymph sac of the frog as soon as the first muscle has been 

 prepared and removed so that the other gastrocnemius may get 

 a sufficient amount of the drug by the time that it is wanted. 

 Secure a record of the contraction of the muscle first pre- 

 pared, using the spring-driven kymograph. Now prepare the 

 second gastrocnemius and obtain a contraction in a similar 

 fashion. From time to time take other records to discover 

 when the veratrine effect disappears. 



Compare the contractions of the normal and veratrinized 

 muscles. 



