ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 91 



Finally, we have the observations of Eollett (48) on 

 the very different contraction curves exhibited by Dytiscus and 

 Hydrophilus. The fresh muscle of Dytiscus far exceeds that of 

 Hydrophilus in regard to rapidity and energy of single twitches, 

 but with prolonged activity the energy of its contractions soon 

 gives way, and this is in a much more marked degree than their 

 rapidity, although the latter also diminishes considerably. The 

 more sluggishly contracting Hydrophilus muscle, on the other 

 hand, maintains its energetic twitches at a comparatively high 

 level, even after prolonged activity ; in the process of fatigue, 

 however, they become more and more extended, so that their 

 duration may finally last twenty times longer than the contraction 

 of fresh muscle. 



As \vas said above, the muscle - fibres of the heart are 

 distinguished by abundance' of sarcoplasm, which may well be 

 connected with their extraordinary vitality in many cases. 

 Panum observed rudimentary pulsations of the heart in rabbit 

 up to 15^ hours, Vulpian in the mouse to 46, in the dog to 

 96 hours, after death (!). Single fibres of the cardiac muscle 

 of mammals examined in physiological salt solution will often 

 exhibit unmistakable rhythmical pulsations the day after death 

 (Sigm. Mayer). 



In all these cases, temperature exerts the greatest influence 

 upon the total duration of existence, or the steepness of decline 

 of excitability, both in isolated muscle and in the still living 

 animal. This is intelligible when we remember the great 

 significance of temperature for the intensity of all processes of 

 metabolism, and, in particular, for that of autonomous dissimila- 

 tion. We should therefore expect a 'priori that the death and 

 corresponding decline of excitability would, as a rule, occur 

 more rapidly with high than with low temperature. The effect of 

 temperature is more positively marked in cold than warm- 

 blooded animals. 



Du Bois-Eeymond has found gastrocnemius and triceps 

 muscles of frog that were still excitable at C. ten days after 

 excision, while on a hot summer day excitability will disappear 

 after 24 hours, and with medium temperature at about the third 

 day. The data in this respect are insufficient in regard to skeletal 

 muscle in \varm-blooded animals. On the other hand, there are 

 interesting observations on mammals as to the extraordinary re- 



