48 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



directly behind the line where the edges of the paper have been glued 

 together. Without removing the writing lever from the drum, revolve 

 the latter to this line. By means of an alcohol lamp gradually raise 

 the temperature in the muscle chamber to 5 C. Make the current. 

 Allow the drum to revolve, and when the writing lever has passed the 

 first contraction, open the circuit. Again rotate the drum to the 

 aforesaid line; adjust the writing lever in the abscissa, and heat to 

 10 C. Make the current and allow the drum to revolve, again break- 

 ing the circuit directly after the second contraction. Repeat this pro- 

 cedure at intervals of 5 degrees up to 40 C. Contrast the sluggish 

 contractions obtained at low temperatures with the rapid twitches 

 obtained at higher temperatures. Is the increase in the height and 

 decrease in the length of the individual contractions uniform? 



Increase the temperature still further, and revolve the drum by hand 

 a little at a time. At about 43 C. the frog's gastrocnemius enters the 

 state of heat-rigor, and finally shortens maximally. Remove the 



FIG. 27. EFFECT OF CHANGES IN TEMPERATURE ON MUSCULAR CONTRACTION. 

 The temperature was raised 5 degrees each time. 



muscle from the chamber and examine its texture and appearance. 

 Stimulate it and ascertain whether it contracts. 



Annotation. By attaching an automatic key to the kymograph the current 

 may be broken precisely at the same moment. This permits the individual con- 

 tractions to become superimposed (Fig. 27). 



2. Influence of Chemicals on Contraction. Inject a few drops of 

 a 1 per cent, solution of veratrin sulphate into the dorsal lymph-sac of 

 a frog. Wait fifteen minutes. Prepare the gastrocnemius muscle in 

 the usual manner, and fasten the femur in the clamp. Attach its 

 tendon to the writing lever, and arrange the inductorium for stimula- 

 tion with single induction shocks of moderate strength. Record several 

 contractions upon a rapidly revolving drum. Study the character of 

 the contraction of the veratrinized muscle. Wherein does it differ 

 from the contraction of normal muscle? Also note that the veratrin 



