5B6 Sir E. Home on the influence of the Nerves, &c. 
This influence of the nerves upon the arteries, throws con- 
siderable light upon some of the most important actions in the 
animal economy. By its means the same arteries, at different 
times, allow very different proportions of blood to pass through 
them, and those employed in furnishing blood for the secre- 
tions have the supplies regulated, which explains the use of 
the system of nerves with which the blood vessels of the vis- 
cera are so abundantly furnished. 
The erection of the penis, produced by a particular state of 
mind, is one of the effects of this influence of the nerves upon 
the arteries, and the stoppage of the secretions from the same 
cause is another of an opposite kind. 
The ready supply of blood to a limb by the small anasto- 
mosing branches, when the principal arterial trunk is oblite- 
rated, depends upon the same cause; and the coagulation of 
the blood in the arterial trunk leading to a mortified part, 
arises from the nerves having previously lost their influence over 
it. On this dominion of the nerves over the actions of arteries 
depends the growth of the body, the regeneration of parts in 
those animals in which it occurs, as lizards and others, and 
the formation of tumours of all the different kinds. The cir- 
culation of the blood is therefore no longer to be considered 
as wholly dependent upon the heart and the elasticity of the 
arteries, for although by these alone it can be kept up, the 
action of the nerves is necessary to regulate the distribution 
of the blood to the different parts of the body, accordingly as 
supplies are wanted to carry on the necessary operations of 
the animal economy. 
