. A text-book of human physiology . therefore to have the power ofregulating the amount of work done under a givenstimulus, -according to the requirements of the must forego a complete theoretical disciission ofthese facts here; but we would direct attention to thesignificance of the red fibers in this connection. Theyare, as it appears, the most important source of theadditional work done as the result of an increasedtension. Thus we find that the secondary lift due tothese fibers, in contractions against a tense spring in-27 438 THE FUNCTIONS OF CROSS-STRIATED MUSCLES creases as the
. A text-book of human physiology . therefore to have the power ofregulating the amount of work done under a givenstimulus, -according to the requirements of the must forego a complete theoretical disciission ofthese facts here; but we would direct attention to thesignificance of the red fibers in this connection. Theyare, as it appears, the most important source of theadditional work done as the result of an increasedtension. Thus we find that the secondary lift due tothese fibers, in contractions against a tense spring in-27 438 THE FUNCTIONS OF CROSS-STRIATED MUSCLES creases as the tension rises, whereas the primary lift caused by the whitemuscle fibers, decreases as a rule with a rising tension (cf. page 436). 3. The Absolute Power of a Muscle.—The method of after-loading- has beenused for the purpose, among other things, of determining the so-called absolutepower of the muscle. A muscle is loaded only with a lever, and the lever issupported mechanically so that the weights hung on it, which constitute the. Fig. 176.—Isotonic (upper) anil isometric (lower) contraction curves under the same primarytension, after Fick. To be read from left to right. The curves a, b, c, d, represent the short-ening of the corresponding to the isometric contractions a, ^, y, S. after-load, do not affect the muscle so long as it is resting. It is loaded bythe weights oidy when contraction begins, and lifts them only when its tensionovercomes the after-load. By adding weights one reaches finally a mass whichthe muscle no longer has the power to lift. This weight is taken as the absolutepower of the muscle (E. F. Weber). It is evident that, other things being equal, the absolute power of a musclemust be proportional to its cross section, or in other words, among muscles com-posed of the same kind of fibers the thickest is the strongest. In tetanus theabsolute power is greater than in simple contractions, and for the voluntary SIGNS OF ACTIVITY IN MUSCLE AND NERVE 43
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