1883.] Variations of Latency in certain Skeletal Muscles. 291 



been discussed in our previous paper, and need not occupy us here ; 

 from a physiological point of consideration these are in the economy 

 of the living animal liable to smaller variations, and therefore of less 

 interest than the effect of change of temperature and fatigue. 



Physiologically considered, the weight raised when the muscle is in 

 service will be constant for the individual, when the stimulations are 

 equal. The researches of Navalachin have shown that most work is 

 done and less fatigue produced when stimulation sub-maximal in 

 character is applied to the frog's muscle, and no doubt the muscle in 

 service during life is usually excited by sub-maximal stimulation (in 

 an electrical sense). It is important to bear in mind that a constant 

 weight used in a series of experiments bears a different relationship 

 to the muscle of a frog weighing x grms. or x + or x — grms., 

 inasmuch as it affects variously the elasticity of the stronger or 

 weaker muscle. In highly extensible parallel-fibred muscles with a 

 small limit of elasticity, such as the hyoglossus, the divergencies 

 obtained by incommensurate weightings are very considerable. 



Our experiments tend, we think, to support the idea which has 

 been expressed by many physiologists, that the relationship between 

 length of latency and the conditions of elasticity and extensibility of 

 the muscle is a close one. 



Conclusions. 



1. The limits within which the normal latency varies (intentionally 

 introduced extrinsic influences apart) appear to be as follows : — 



a. In gastrocnemii of various frogs at different seasons — 



Bana temp. -008"— -0208." 



b. In different muscles of the same animal — 



Frog .. '008" (gastrocnemius) to "022" (hyoglossus). 

 Toad .. -012" (triceps) „ -024/' (hyoglossus). 



Tortoise "022" (omohyoid) „ -036" (ext. dig. com., &c). 



(The complete exclusion of certain influences, nutritive, thermal. 

 &c, is impossible.) 



2. Conclusions as to the length of the latent period based on the 

 duration of the contraction are liable to error ; especially is this the 

 case when we attempt to reason for one class of animals' from the 

 relationship found in another. 



3. The duration of the latency increases and decreases in direct 

 but unequal proportion to the amount of weight which the muscle 

 has to lift. 



4. Increase in strength of stimulation is accompanied by a shorten- 

 ing of the latent period. The variation seems to depend on the 

 absolute strength of the stimulus employed, viz. : (a) Increase from 

 minimal to stimulation giving rise to maximal contraction is accom- 



