598 
ON ARTERIAL AN1) VENOUS BLOOD. 
restored. It is not so if a vein be opened, for it does not necessa- 
rily follow that the arteries of a part increase in activity in order 
to supply the blood abstracted from the vein . Both these facts 
are confirmed by observation. If one of the carotid arteries be 
tied, almost immediately the temporal and occipital branches of 
the carotid of the opposite side may be distinguished through 
the integuments, dilating themselves, becoming tortuous, and 
struggling, as it were, to circulate an additional quantity of 
blood. 
I was first led to remark this in the case of a child, on whose 
carotid artery I had placed a ligature for the cure of a large 
nsevus on the cheek. Almost immediately after the operation, I 
observed the arteries from the opposite side of the head enlarging, 
increasing in their action, becoming tortuous, and actively em- 
ployed in supplying the place of those vessels whose channels 
had been obstructed. Indeed, it was the knowledge of this 
power in the anastomosing branches, when a trunk is obliterated, 
that led Hunter to perform the “high operation,” as it is called, 
for popliteal aneurism. The same phenomenon is exhibited in 
the eye. If an artery on the sclerotic conjunctiva, passing into a 
speck on the cornea, be divided, immediately vessels will be 
perceived, stretching across the cornea from the opposite side, to 
supply the place of the vessel which was divided. 
The whole arterial system, by a wise provision of nature, when- 
ever the supply of blood to one part is diminished, makes an 
effort to throw blood by another to the part which has been de- 
prived of its natural quantity, and thus the action of the heart 
and arteries must be more or less injured ; whereas the abstrac- 
tion of blood from a vein is followed by no such increased action 
of the arterial system, — there is no local diminution in the supply 
of arterial blood, — no effort made by the arteries to supply the 
place of the venous blood which has been removed. On the con- 
trary, a diminution in the supply of blood to the heart by the 
veins will, as I have just observed, have the effect of diminish- 
ing the vigour of the heart’s action, and also that of all the arte- 
rial system. 
The effects of opening the temporal artery in puriform oph- 
thalmia may be instanced, as well illustrating the difference be- 
tween arterial and venous depletion for the cure of inflammation. 
An eye injected with red vessels will be suddenly relieved by 
opening the temporal artery, and the conjunctiva will become 
quite pale, inducing one to suppose that the inflammation is 
subdued. But I have generally found that, sooner or later, even 
in a few hours, the inflammation has returned; and I think 
others, particularly Dr. Veitch, have made the same remark. 
