116 LETTERS TO BROTHER JOHN. 



accordingly as surrounding pressure and support 

 are removed from the nerves. 



But a state of the body the very opposite to that 

 just described is alone favourable to CONTRAC- 

 TILITY : for I have before proved that vigorous 

 CONTRACTILITY can only reside in recently orga- 

 nized matter ; and in order that this recent orga- 

 nization this perpetual youth, as it were of the 

 several parts of the body may be kept up, an 

 abundant supply of healthy blood is absolutely 

 indispensable. Thus CONTRACTILITY in perfection 

 requires a highly-distended condition of the blood- 

 vessels, and, consequently, a firm and compact state 

 of the body a state exactly the contrary of that 

 just described as favourable to the development of 

 SENSIBILITY. Hence arises a most important corol- 

 lary; viz. that whatever increases the natural vigour 

 of the circulation, increases the CONTRACTILITY and 

 lessens the SENSIBILITY of the body; and whatever 

 lessens the SENSIBILITY of the body, by increasing 

 its CONTRACTILITY, increases also the natural vigour 

 of the circulation ; since the blood is circulated by 

 virtue of the contractile power of the heart and 

 arteries. 



The degree of SENSIBILITY, therefore, is always 

 not only in an inverse ratio of the degree of CON- 



