90 ELECTRO-PHYSIOLOGY CHAP. 



separation from it. We learn from experiment that every muscle 

 which is excised and therefore deprived of normal conditions 

 of nutrition, will sooner or later lose its excitability and become 

 moribund. The interval at which this occurs is very unequal in 

 different animals, even in the muscles of the same animal it 

 varies considerably with external conditions. In any case we 

 must assume that the autonomous equilibrium of the muscle- 

 substance is permanently disturbed from the moment of its 

 separation from the organism, since, in consequence of the less 

 favourable conditions of assimilation with prolonged dissimilation, 

 a constantly increasing autonomous " down " change ensues, as 

 expressed in diminished excitability. As a general rule, we find 

 that the muscles of cold-blooded animals preserve their excita- 

 bility longer than those of warm-blooded animals, in consequence 

 of their lower intensity of metabolism ; yet this law is by no 

 means universal. The muscles of fishes, for instance, seem to 

 lose their excitability very quickly when separated from the 

 organism (46). The expression " cold -blooded" further in- 

 cludes the Invertebrates, many of which (e.g. insects) possess 

 muscles that perish very rapidly. It is noticeable that the 

 muscles of the same animal do not all become moribund and lose 

 their excitability with equal rapidity. If the sarcoplasm really 

 posseses a nutritive function, as was shown above to be very 

 probable, we might expect that the sarcoplasmic dark muscles 

 would, as a rule, be fatigued and die less quickly than the 

 a-sarcoplasmic clear muscles. According to Griitzner's obser- 

 vations this actually is the case. Eanvier observed long 

 ago in the triceps hunieri of rabbit, which consists of pale 

 (clear) and red (dark) fibres, that it responds at first like a pale 

 muscle owing to the lesser excitability of the white fibres, but 

 when fatigued with prolonged excitation it contracts like a red 

 muscle, because the white portion is fatigued, while the red is 

 still capable of serving. This difference also comes out very 

 clearly in the fact that, according to Bierfreund (47), pale 

 muscle falls into rigor mortis much more quickly than red muscle. 

 Under the same conditions the first becomes rigid in 1 3 

 hours, the latter only in 11-15 hours after death. And when 

 the rigor of the pale muscles has already passed off again 

 completely (10-14 hours after death), the red muscles have 

 not begun to lose their rigidity. 



