OF VITAL MOTION. 61 



the blood, is determined by the withdrawal and not 

 by the communication of a stimulus. 



It may be presumed, in the next place, that the 

 dartos will contribute towards the knowledge of mus- 

 cular action, for this tunic is closely allied to true 

 muscle both in structure and function. In the dartos, 

 moreover, there are few nerves and vessels, and there- 

 fore the phenomena of irritability may be supposed to 

 be simple and intelligible, and not complicated by 

 those agencies which obscure the secret action of true 

 muscle. Here, indeed, it seems as if the problem of 

 mobility were stated in the simplest terms, and 

 the result made known as clearly as possible. What 

 these are we may learn in the first chapter, where it 

 is shown that the state of contraction is associated 

 with the operation of cold, and the state of relaxation 

 with the presence of warmth. Contraction, indeed, 

 in relation to the antagonistic phase of relaxation, 

 is seen to be a phenomenon connected with the 

 withdrawal, and not with the communication of a 

 stimulus. The true connexion of contraction in the 

 dartos with the analogous phase of muscular activity 

 cannot now be determined, but if it is such as may 

 be presumed from the anatomical relation of the 

 two structures, the result is very significant, and 

 the more so as it harmonises with what is deduced 

 from the changes in fibrine. 



Under any circumstances the histories of the dartos 



