1883.] Variations of Latency in certain Skeletal Muscles, 281 



and no siphonoglyphe. 5th. The Alcyonidse, a large and somewhat 

 heterogeneous group containing all the remaining genera of the 

 Alcyonaria, which, though exhibiting many wide variations, inter se, 

 agree in possessing no specially marked characters of deviation from 

 an ideal central form from which, I suppose, they must have sprung. 



IV. " On the Variations of Latency in certain Skeletal Muscles 

 of some different Animals." By Theodore Cash, M.D. 

 and Gerald F. Yeo, M.D. Communicated by Dr. 

 Sanderson, F.R.S. Received May 29, 1883. 



In a former paper ("Proc. Hoy. Soc," vol. 33, p. 462) we laid 

 before the Society the results of a series of experiments by which we 

 had endeavoured to ascertain accurately the differences in the dura- 

 tion of the latent period of contraction of skeletal muscle (frog's 

 gastrocnemius) which could be brought about by varying the follow- 

 ing influences : — 



1. The weight of load. 



2. The mode of applying weight (supported or unsupported). 



3. The strength of stimulation. 



4. Temperature. 



5. Fatigue. 



We have since been engaged in determining the relative duration 

 of the latent periods of different skeletal muscles of vertebrate 

 animals. Besides several muscles of the Bana temp., we have 

 examined some from the toad, tortoise, small mammals, and birds. 

 In this paper, which is intended to be a continuation of the one 

 above referred to, we beg leave to lay before the Society the results 

 of these experiments and our general conclusions. 



We know from the works of Fick,* Marey,f Ranvier,J Fredericq,§ 

 Richet,|| and one of ns,^[ that various muscles in the same animal 

 have a mode of contraction differing more or less from one another, 

 and adapted to the kind of work they have to perform. But in the 

 works of most of these authors little information can be found 

 concerning the variations in the duration of the latent period, in dif- 

 ferently contracting muscles, whether those of the same animal or 

 those of different animals. 



* Fick, " Irritabelen Substanzen." 



f Marey, " Du Mouvements dans les Fonctions de la Tie." 



X Ranvier, " Lecons sur le Systeme Musculaire." 



§ Fredericq, " Bull, de l'Acad. roy. de Belgique," lvii, No. 6. 



j| Richet, " Physiologie des Muscles," &c. 



TT Cash, •' Journal of Anat. and Phys.," vol. xv. 



