100 ELECTRO-PHYSIOLOGY CHAP. 



diminution of its store of reserve matters, it will be found that 

 the latter relaxes more rapidly than the former. The one behaves 

 to the other as a cooled muscle to a fatigued muscle. 



There are no satisfactory observations as to the effect of 

 temperature on magnitude and process of contraction in striated 

 warm-blooded muscle, but it has long been ascertained for cardiac 

 muscle both in cold and in warm-blooded animals, that the time- 

 relations of the natural and spontaneous, as also of artificial, 

 contractions, are considerably retarded by cooling, while the con- 

 trary occurs with rise of temperature. The mechanical latent 

 period undergoes similar changes, most conspicuously in the excised 

 heart of warm-blooded animals (A. D. Waller, 55). While at 

 normal temperature (38 40) the contraction apparently begins 

 at the moment of excitation', a latent period being only perceptible 

 on applying more delicate methods of time - measurement, on 

 vigorous cooling (12 0) it may last for more than a second. 

 It is not known whether with uniform stimulation the same 

 relations between temperature and contraction-magnitude obtain 

 in cardiac muscle, as have been demonstrated by Gad and 

 Heymans for striated skeletal muscle. If the normal period of 

 contraction in a muscle is very short, the effect of falling tempera- 

 ture will be well marked, and on the other hand the shortening of 

 the contraction process by warming is conspicuous when the 

 muscle has previously been yielding a sluggish twitch. This 

 is most marked in smooth muscle, where the process of contraction 

 is accelerated in a remarkable degree by heating. 



The behaviour of smooth muscle - elements with varying 

 temperature exhibits many interesting peculiarities, mainly 

 because in many, perhaps all cases, they fall into a state of more 

 or less marked and permanent contraction (" tonus ") independently 

 of the nervous system, the strength of which is conditioned in a 

 marked degree by the temperature of the moment. This is 

 emphatically the case in the smooth muscles of many invertebrates, 

 as well as in poikilo thermic vertebrates. The adductor muscles 

 of the fresh- water molluscs (Anodonta, Unio), e.g., usually exhibit 

 a well -developed tonus, which is certainly independent of the 

 central nervous system. By partially breaking up the shell in 

 large specimens of Anodonta, it is easy after removing the other 

 soft parts to obtain a preparation which is well adapted to all 

 kinds of excitation experiments (Fick, 32 ; Biedermann, 62). At 



