XXXVIII.] - INFLUENCE OF TEMPERATURE, ETC. 213 



7. Marey's Myograph (fig. 132).- The pithed frog is pinned on a cork plate, 

 the tendon of the gastrocnemius is dissected out and attached to a writing- 

 lever, which is weighted with a counterpoise ; the sciatic nerve is dissected 

 out and stimulated in the ordinary way. The cylinder moves on a horizontal 

 axis. The muscle can be stimulated while it is still in situ, and is under 

 more normal conditions than in the case of an excised muscle. It is useful 

 for the study of the action of poisons on muscle. 



8. Spring-Myograph of Fredericq (fig. 133^. This is arranged in the same 

 way as the spring-myograph, but the glass plate is placed horizontally. The 

 glass plate is pulled along rapidly by a band of caoutchouc. A key in the 

 primary circuit is opened by means of a pin attached to the frame carrying 

 the glass plate when the plate is discharged. In an improved form of the 

 instrument, a steel rod made to vibrate at the moment the plate is discharged 

 records a time-curve beside the muscle-curve. 



LESSON XXXVIII. 



INFLUENCE OP TEMPERATURE, LOAD, AND 

 VERATRIA ON MUSCULAR CONTRACTION. 



1. Influence of Temperature on Muscular Contraction. 



(a.) Arrange the nerve- muscle preparation on a crank-myograph 

 after-loaded as in Lesson XXXV., using the automatic key by 

 means of the drum. All the curves are thus taken on the same 

 ahscissa. Take a tracing at the normal temperature of the room. 

 Mark the moment of stimulation. 



FIG. 134. Showing how the form of a Muscle-Curve varies with the temperature of the 

 water flowing through the box, shown in fig. 119. i at 5 C. ; 2 at 10 ; 3 at 15; 

 4 at 20 ; 5 at 25 ; 6 at 30 ; ^ at 35 ; and 8 at 40 C. The lowest tracing indicates 

 time, ioo D.V. per second, x the moment of stimulation, by automatic break. 



(b.) Place ice upon the skin over the gastrocnemius for some 

 time, or pour iced salt solution on the exposed gastrocnemius, and 

 then take another tracing on the same abscissa, noting the differences 



