128 ELECTRO-PHYSIOLOGY CHAP. 



(triceps, gastrocnemius) the height of twitch to that of tetanus is as 

 1:2-3, the ratio in the same muscle of the toad is about 1:5, 

 and it is considerably larger in the more sluggish muscles (hyo- 

 glossus and rectus of frog, 1:89). In investigating isometric 

 muscular action in man (M. obductor indicis or interosseus dorsalis 

 primus) by a specially constructed tension indicator, Tick (16) 

 found, on comparing the tension produced by a maximal single 

 stimulus with that developed by tetanising excitation, that the 

 latter is ten times as great as the former, while in the frog the 

 difference is much less, whether in isotonic or isometric action. 

 Human skeletal muscle therefore reacts in complete correspondence 

 with red sluggish fibres. 



Bearing in mind these results, which show that the work 

 yielded in tetanus by the quick (pale, clear) muscles is insignificant 

 both as regards size of weight lifted and height to which the 

 load is raised, in comparison with the same yield of the sluggish 

 (dark, red) muscles, we may adopt Griitzner's denotation of the 

 latter as "tetanus muscles," since they may be said, through 

 their physiological properties, to be adapted to this form of shorten- 

 ing, and singularly fecund in their response. When quick and 

 sluggish fibres are united in the same muscle, it may result from 

 the differences of excitability as above, that with weak excitation 

 (direct, or from the nerve) different portions of the muscle twitch, 

 or go into tetanus, from those brought into play with stronger 

 excitation. Griitzner is even inclined to ascribe the summation- 

 effect in tetanus in great part to these differences in the physio- 

 logical response of the two kinds of fibres. He refers (11, p. 250) 

 the striking similarity between a series of " supported " twitches, 

 and tetanus (supra), to an internal supporting of the muscle by 

 its sluggish (dark, red) fibres. These keep it at rest at a given 

 medium length, which naturally decreases inversely to the number 

 of red fibres. If an appropriate stimulus, i.e. not too powerful, 

 is sent into the muscle when thus shortened, its excitable (light) 

 portions will contract visibly. This second superposed contraction 

 must accordingly result more quickly, as v. Kries found actually 

 was the case (shortening of apex - time). The stronger the 

 stimulus, however, the greater will be the activity of the more 

 sluggish portions ; the more rapidly will the discontinuity vanish 

 (which, as might be expected, is disputed by Kohnstamm), and 

 the greater will be the height of the " tetanus curve." 



