288 



Dm T. Cash and Gr. F. Yeo. 



[June 14. 



of investigation pursued by experimenters, as well as to the widely 

 varying resnlts which they have obtained. It seemed to as. therefore, 

 that time devoted to a systematic examination with one exact method 

 of the many aspects of the subject wonld be advantageously employed, 

 and wonld furnish resnlts relatively correct, and of a value which 

 would be greater than could be obtained by grouping the conclusions 

 of numerous authors, whose methods and objects of research differed 

 and who had no unanimous starting point for their investigations. 



For the gastrocnemius of a frog : 



Helmholz* gives as a latency , '01" 



Placej and (jad* -OlU" 



whilst Mendelssohn. § who has admirably grouped the results obtained 

 by these and other authors, found that in frogs taken at random of 

 various sizes and in different seasons, the latency varied within the 

 wide limits of "00-1" — 012". Xavalachin'-'. who has ably investigated 

 the production of heat during the active contraction of striated 

 muscle, has pointed out that the latency of the frog's gastrocnemius is 

 shorter in the spring than in the summer months. Here vre have to 

 do with another element rather than with temperature — namely, 

 with the spawning of the animal, the most disturbing internal 

 influence to which a frog is liable. The latencies before and 

 after spawning are various, the irritability of the muscles being 

 different. This is in its effect almost convertible with the experience 

 of Helmholz, Engelmann, Lautenbach. and others.*" who have pointed 

 out that increase in strength of stimulation shortens the latency. In 

 the spring-time the irritability of the animal is increased, and maxi- 

 mal stimulation, which in the summer frog would produce a certain 

 definite effect, is here hyper-maximal <^so to speak) and the latency is 

 correspondingly shortened. To the same reason, i.e., an increase in 

 irritability. Mendelssohn looks for the explanation of the shortened 

 latency of the muscle, whose nerve has just been divided. VTe must, 

 however, confess that we are unable to confirm his results, i.e.. that the 

 latency in the case of the muscle of which the nerve has just been 

 divided, may be temporarily shortened by half, in the case of the 

 Rami temp. The latency given by Gad ("004") associated with a 

 lengthening of the muscle as precursor to its general contraction, we 

 cannot attempt to criticise, as we have very rarely ourselves seen the 

 form of curve he represents as beino- normal, but which he oniy 



* Helmholz, " Midler's AtcMt," 1850. 



f Place, !; Xederland AtcMv v. G-enees, en !N"atuur." III. 1867. 



% G-ad, " Ueber das Latenzstadiiim, &c." " Archiv f. Anat. und Phys.." 1S79. 



§ Mendelssohn. "Marey's Travaux." 1S7S-9. 



|| JfaTalachin, " Myotbermiscbe Cntersuchungen." " Pniiger's Arch.," Bd. XIV. 

 ^ See Tables IT and T in former paper. 



