On the Latent Period of Muscle Contraction. 475 



tion, and an abridgement of the former of more than the of a 

 second is readily produced by strong stimulation, without inflict- 

 ing permanent injury upon the muscle. With stimulation of a much 

 milder character, more closely related to physiological stimulation, a 

 very slight shortening of the latency may be observed. 



7. When Helmholtz was investigating the speed of motor nerve con- 

 ductivity, he found that in the case of man this underwent a remark- 

 able change in the summer time, so that its velocity became 60*50 

 metres per second, or fully twice as much as it had been some time 

 previously. This acceleration he attributed to the elevation in atmo- 

 spheric temperature occurring at that season, and this conclusion led 

 him to a theory for the different speeds of conductivity in the upper 

 arm when the nerve is sheltered and the lower when it is more super- 

 ficial. 



Troitzky, who investigated conduction in the nerve of the frog, 

 stated that the speed was greatest between 10° and 20°, and diminished 

 both under lower and higher temperatures. 



It will be recollected that our moist chamber was furnished with 

 a coil of tubing, which acted as means of producing heat or cold 

 according to the temperature of the fluid passed through it ; by means 

 of this coil we were able to produce as extensive variations of heat or 

 cold as our subject demanded. Water cooled by a mixture of chipped 

 ice and salt in the one funnel, and water heated somewhat above the 

 temperature we desired to produce in the other, enabled us by their 

 conjoined use to hit the point we needed with precision. The atten- 

 tion of one of us was fixed upon the thermometer, and at a sign from 

 him that the mercury stood at the desired level, the pendulum was 

 liberated and the curve registered. 



Some experiments were made to ascertain the effect upon exposed 

 nerve of the temperature of the chamber, and with the results of 

 these we will begin this section of our subject. 



Our Table (VI) shows the effect of a depression of the tempera- 

 ture through 12° 0. (from 17° to 5°) and of its subsequent elevation 

 through 8° (17° to 25°) or of a total excursion through 20°. The 

 variation of latency accompanying this change is from '026" (5°) to 

 •0127" (25°), or no less than '0133" or the y 1 ^ part of a second. 

 Having taken a curve at the room temperature (17° C), we rapidly 

 cooled down the muscle to 5°, and then permitting it gradually to 

 regain its normal a curve was taken at each degree; when 17° was 

 reached we began to heat slowly till we had raised the temperature to 

 25°. 



VOL. XXXIII. 



