290 



Drs. T. Cash and G. F. Yeo. 



[June 14,. 



some unstable cause not usually operative. We have seen such 

 muscles allowed again to cool to the room temperature fail to give 

 again the long initial latency at first manifested, whereas, as a rule, 

 the result obtained from a given temperature for the same muscle is 

 constant or nearly so, should heating and cooling not have been carried 

 to a deleterious extent. We cannot regard a muscle, showing a long 

 latency and a long curve, as being in both respects in series with a 

 more quickly contracting muscle, cooled down through a certain 

 range of temperature. One of the most important features in the 

 divergence, is in the change of elasticity in the case of the cold 

 muscle, but beyond this we have variations of kind between muscles 

 which must help to account for the intimate relationship between the 

 latency and curve in any given muscle. 



Fatigue. — M. Ranvier has recorded the remarkable fact that the 

 latency of the thoroughly fatigued red muscle of the rabbit, may 

 bear the proportion to that of the fresh muscle of nearly five to one. 

 He says, if the strength of the stimulation is increased, the latency 

 shortens again, as contractibility is redeveloped. Since the fatigued 

 muscle is equally elastic, but less irritable than the fresh muscle, a 

 stimulation which at first produces a maximal result, soon becomes 

 sub-maximal, then minimal, and finally ceases to be effective ; so that 

 constant increase of stimulation is required to elicit an equal (in the 

 sense of a maximal) effect. Mendelssohn has described an increase of 

 latency from "008" to "03" in the gastrocnemius of the frog as the 

 result of fatigue. These extensive variations are quite possible, but it 

 not infrequently happens that the length of the latency is rather 

 apparent than actual as a result of fatigue. A careful examination 

 of the curve of a fatigued muscle will often enable us to determine 

 a very gradual but definite departure of the lever attached to the 

 muscle from the abscissa, in what, at first sight, seemed to be the 

 actual latency. This would be concealed by a thick abscissa, or lost 

 by the use of a too slightly amplifying lever. 



In our former paper we gave tables showing that 1,300 induction 

 shocks (producing maximal single contractions), increased the latency 

 •00526", and that two minutes' tetanus had the effect of lengthening 

 this period '0066". We also pointed out that it is in the extreme of 

 fatigue that the rapid increase in the latency occurs. Exercise short 

 of distinct fatigue was seen even to shorten the latency to a slight 

 extent. This may have been in part due to the increase of extensi- 

 bility which Yolkmann has shown occurs in earlier stages of fatigue 

 of the muscle. In the later stages of fatigue, however, the extensi- 

 bility decreases as the elasticity of the shortened muscle increases, 

 and here we have a corresponding increase in the latency. 



The effects of variations of strength of stimulation and in the 

 amount of weight employed, and the manner of employing it, have 



