EFFECT OF TEMPERATURE 



47 



5. As the load was the same throughout the series of twitches, 

 the total work performed in the several cases is proportional to the 

 heights of lift, and therefore shows the same variations as those pointed 

 out in 4. If, however, we examine the work from the point of view 

 of the rate at which it was performed we see from the figures of the 

 last column that there is a progressive increase in the rate of work- 

 ing which is particularly marked when the relative minimum height 

 at 20° C. has been passed. These rates of work are calculated, as 

 previously described (p. 35), by dividing the amount of shortening by 

 the time of contraction and multiplying by the load, which in this 

 instance was one gram. 



For purposes of comparison in fig. 50 is reproduced a similar 

 series where the gastrocnemius was employed. The arrangement of 

 the apparatus was slightly different, being the one figured on p. 112, 

 the muscle being fixed in the position at which the heart is there 



Fig. SO. — Twitches of a Gastrocnemius at Different Temperatures. 

 Tracing, 200 per sec. Magnification, 5. 



Time 



attached. The time tracing is 100 per sec, and the drum was moved 

 at a rather slower rate. The general result is the same as in the 

 previous example ; but it is to be noticed that there is no relative 

 minimum of height of twitch at 20° C. 



To complete our account of the influences of temperature upon 

 the twitch there are one or two other facts known which do not 

 appear in these tracings. It is found that if the temperature be still 

 further lowered the total height of twitch is still further increased, 

 and the relaxation much more markedly prolonged, and, as 0° C. is 

 approached, there is a rapid change in the direction of diminution 

 in the amount of contraction, till at last none is produced. If, on the 

 other hand, the temperature be still further raised the amount of con- 

 traction increases until about 32° C. is reached : from this tempei'a- 

 ture the height rapidly diminishes, until the muscle goes into heat 

 contraction at 34° C. The twitches at the higher temperature are of 

 the same total duration, although their height is less. 



