28 THE BEGINNINGS OF LIFE. 



action of a stimulus, and without any intervention of the 

 nervous system. The contractility is, however, closely 

 related, and more or less proportionate in degree, to 

 the supply of arterial blood circulating in the capillary 

 vessels with which it is furnished. The experiments 

 of Longet l on this subject are most instructive. He 

 found, as a result of experimentation upon many ani- 

 mals, that all traces of contractility after the direct 

 application of a stimulus disappeared from muscles 

 which had received no arterial blood for a space of two 

 hours j but that almost as soon as the afflux of arterial 

 blood to the muscle was again permitted even in the 

 space of a few minutes the contractility of the muscles 

 again manifested itself upon the application of a stimu- 

 lus, either direct or indirect. But those heat-liberating 

 chemical reactions the processes of combustion neces- 

 sary for the continuance of the nutritive changes are 

 carried on in the capillaries of the muscle as well as in 

 the capillaries of other parts of the body ; and it would 

 seem that the disappearance of the property of contrac- 

 tility from the muscle is dependent upon that stoppage 

 of the heat-evolution therein which the arrest of the 

 circulation entails. In support of this view, on the one 

 hand, it has been shown by M. Becquerel 2 that the 

 temperature of a muscle becomes sensibly lowered when 

 the artery supplying it is compressed and, on the other, 



1 ' Trait^ de Physiologic,' 3me ed. 1869, t. ii. p. 613. 



2 ' Ann. de Chimie de Physique,' 1835, t. lix. p. 135. 



