26 THE BEGINNINGS OF LIFE. 



enough heat to maintain the animal at its proper tem- 

 perature. This conclusion was afterwards confirmed by 

 many other experiments and observations. The re- 

 searches of Lavoisier still left us in doubt, however, as 

 to whether the combustion of the materials of the blood 

 took place in the capillaries of the body generally, or 

 in those of the pulmonary circulation. This doubt was 

 removed by Spallanzani; and the subsequent experi- 

 ments of Magnus and of Claude-Bernard only tended to 

 confirm his conclusion, that the heat-producing chemi- 

 cal changes were carried on in the capillaries of the 

 body generally. Thus the heat evolved in animals is 

 some of that solar heat which had previously impinged 

 upon plants, and which was gradually locked up in the 

 form of potential force, during the growth of the plant- 

 tissue subsequently taken as food by animals. 



2. Turning now to the next dynamic manifestation of 

 animals to their power of movement we may, for the 

 sake of brevity, consider this as it presents itself in the 

 higher animals only in those in which the movements 

 depend upon the contractility of definite structures 

 known as c muscles. 5 Contractility is the essential attri- 

 bute of the muscle, and, being one of the peculiarly 

 vital endowments, we may now enquire how far this 

 vital property is one which is correlatable with ordinary 

 physical forces, or whether it can display itself inde- 

 pendently of these \ In the first place, it is important 



1 For a full and admirable treatment of this question we must refer 

 the reader to pp. 120-194 of the work of Gavarret, already quoted. 



