INTRODUCTION,. S3 



tary transmutations, for in truth the object of the 

 one is but to produce the other. 



Of the active forces of the Animal Body. 



The muscular fibre is not merely the organ of vo- 

 luntary motion. We have just observed, that it 

 is moreover one of the most powerful agents adopted 

 by nature for the operation of carrying on those 

 motions and transmutations necessary to vegetative 

 life. Thus the fibres of the intestines produce the 

 peristaltic motion, whereby the chyle is driven into 

 the orifices of the lacteal veins, and the faeces are 

 protruded. The fibres of the heart and of the arte- 

 ries are the agents of circulation, and thereby of 

 every other secretion. 



Volition, as has been also noticed, causes a fibre 

 to contract, through the instrumentality of the cor- 

 responding nerve. The fibres not directly subser- 

 vient to volition, such as those just instanced, are 

 nevertheless affected also by the nerves which ex- 

 tend to them ; hence arises a probability that the 

 nerves also are the proximate causes of their invo- 

 luntary contraction. 



Every contraction in the animal frame, and indeed 

 every change of dimension that we observe in mat- 

 ter in general, is operated through the instrumen- 

 tality of chemical changes. Some fluid without 

 momentum, such as caloric, appears by its flux and 

 reflux to be the prime agent in these cases, as it 

 assuredly is in the more violent convulsions and 



Vol. I. D 



