On the Latent heriod of Muscle Contraction. 403 



they saw the speed decreased to a great extent when the nerve was 

 laid upon ice, and even slight variations in the room temperature 

 sufficed to produce material changes. Troitzky* came to the conclu- 

 sion that conduction is the most rapid in the frog's nerve between 10° 

 and 20° C, and diminishes both by higher and lower temperatures. 

 The influence of temperature could, however, he concluded, be subor- 

 dinated to a certain extent by increasing the strength of the 

 stimulation. 



That a powerful shock is more potent to induce rapid conduction 

 than a weaker one has been upheld by Yalentinf and von "Wittich 

 as well as by Troitzky, but has been denied by Rosenthal J and 

 Lautenbach.§ These interesting results would have been still more 

 valuable had accurate corrections been made for the variations in 

 the rapidity of the initial changes taking place in the muscle itself 

 during the latent period, for, as Hermann suggests, changes in the 

 strength of the stimulus may cause these variations to be con- 

 siderable. 



An instrument, designed by du Bois Reymond — the " Frosch- 

 Unterbrecher " — has made the fact apparent that the period of latent 

 energy elapsing between stimulation and obvious contraction also 

 increases if increasing weights, acting as " after- weights," be laid in 

 the supported pan suspended from the muscle. Thus, whilst at lever- 

 tension — at which point the support was fixed — the latency may be 

 less than y-i-g- second, under a weight of 200 grms. it may be more 

 than twice as much. It is evident that whether the muscle be "free- 

 weighted " or " after- weighted," until it has reached a state of 

 counterbalancing tension as regards the weight it is to raise, no ele- 

 vation from the abscissa can be effected. The free- weighted muscle 

 is already stretched as regards the greater number of its fibres by a 

 small weight (30 — 40 grms. for gastrocnemius of frog), whilst the, 

 after-weighted has to attain a similar state of tension before it can 

 commence its true lift. Variations in latency are then to be expected 

 according to the connexion in which we place the weight and the 

 muscle. Place|| and Klunder^f remark that if, after a muscle has 

 been powerfully extended, and while it is returning, by reason of its 

 elasticity, towards its normal condition, a stimulation be applied, the 

 latency may become as short as the — second, a result 

 which Haidenhain** inclines to attribute to the pernicious effects of 

 the previous tension. 



# " Arcli. fur d. ges. Physiologie," viii, s. 599, 1874. 



f Moleschott, " Untersuchungen," x, s. 526, 1866. 



% " Monatsbericht d. Berliner Acad.," s. 419, 1875. 



§ " Archiv. d. Science Phys. et Nat.," Juli, 1877. 



|| " Handbuch der Physiologie," Bd. 2, p. 24. 

 " Nederlandsch Arch. y. Oenees en Naturk.," iii, p. 177, 1867. 

 ** " Untersuchungen aus dem Kieler Institut," p. 101, 1868. 



