294 EEPORTS ON THE STATE OP SCIENCE. 



relaxation, is a recuperative process, which places a muscle that has 

 once contracted in a position to contract again. 



(1) Previous activity is then liable to modify the contraction pro- 

 cess, as in the case of the staircase, by modifying the transmission of 

 excitation through a muscle — that is to say, by modifying the mode of 

 transmission of electrical charges. Since this transmission depends 

 upon the electrolytes of muscle, we may look for modifications in these 

 electrolytes as due to previous activity, and possibly responsible for 

 many of the best-known incidents in fatigue. 



(2) Previous activity also affects the store of combustible material 

 within muscle, and so greatly modifies its recuperative power. 



As to the manner of the recuperation, which is partially defeated by 

 fatigue, it is possible that there are differences in such different cases 

 as those provided by the muscle of cold- and warm-blooded animals re- 

 spectively. When the recuperative processes of the relaxation period 

 have done their work, there is still need for further recuperation. This 

 is clearly seen in the case of frog's muscle. Thus, I have made sure of 

 the fact, that even the second contraction of such a muscle is modified 

 by the occurrence of the first to a demonstrable degree provided that it 

 is observed within a certain period, much more prolonged than that of 

 visible change, after the occurrence of the first. The second contrac- 

 tion is not only higher (staircase), but is even more clearly prolonged. 

 Oxidations, accelerated by contraction, and these are the whole source 

 of energy, are occurring in this later period of recuperation, just as 

 also in the first recuperative period of relaxation, but are here more 

 clearly seen as alone in action. In what form do such processes provide 

 their energy? Conceivably this energy may be placed at the disposal 

 of the muscle in the simplest way, as so much heat, or as some other 

 form of energy. 



It is in this connection that I have continued an investigation of the 

 relation between temperature and the internal osmotic pressure of 

 muscle, since contraction is probably due to variations in the distribution 

 of this factor within the muscle, but so far without observing any corre- 

 sponding change not similarly producible in any simple solution having 

 none of the attributes of ' muscle.' This investigation has, however, 

 still to be continued into the case of mammalian muscle. 



It is clear that it would militate greatly against the average efficiency 

 of the muscles of cold-blooded animals if their energy was delivered to 

 them in the form of heat, and the only conditions determining an addi- 

 tion or an abstraction of energy were variations in external temperature. 

 The muscle of the warm-blooded animal is more fortunately situated 

 behind the protection of its constant temperature regulation, and is in a 

 better position in this respect. The usual expectation is that muscle of 

 this second class is more complex in its relation to its oxidative sources 

 of energy. It is probable that the fact is the reverse of this, and that 

 the warm-blooded muscle is more simple and does actually owe the 

 physical condition of its internal solutions, upon which the phenomenon 

 of contraction depends, to the heat provided by the processes of oxida- 

 tion. That is to say, that it is conceivable that the maintenance of a 

 constant temperature is alsn to be regarded as the maintenance of a 

 constant bank of energy. 



