ON ARTERIAL AND VENOUS BLOOD. 
599 
Whereas, when, in that disease, a vein in the arm is opened, 
and blood is taken to the full extent, the good effects of such 
depletion are permanent. 
This is, therefore, a distinct and important difference between 
the changes that take place in the action of the vessels of a 
part, when blood has been taken from an artery and from a vein, 
and it explains the difference which I have always found in the 
employment of those two different modes of abstracting blood'; 
It is also extremely probable, that there must be a difference of 
effect from the kind of blood which is taken away, — that the 
removal of a pint of arterial blood will produce a different effect 
on the system from the removal of the same quantity of venous 
blood. What these differences are I do not pretend to know ; 
but one proof that the abstraction of venous blood is the most 
useful in the cure of disease is, that in those natural or “ spon- 
taneous hemorrhages” which are so salutary, such as those from 
the nose and hemorrhoidal vessels, the blood which is discharged 
appears to be chiefly venous. Where leeches and cupping are 
had recourse to, it no doubt happens that they remove both ar- 
terial and venous blood at the same time ; but the circumstances 
under which those operations are performed do not furnish us 
with any opportunity of discriminating the comparative effects 
of the abstraction of venous and arterial blood. Another point 
which we ought to bear in mind is, that the temporal arteries, 
as they pass over the zygoma of the temporal bone, can only be 
once opened at the proper point for the operation ; for arte- 
riotomy is not like venesection, — the wound made in the vein 
uniting, and leaving the canal of the vessel entire ; whereas 
when an artery is opened, it is requisite, after taking the neces- 
sary quantity of blood by the wound, to divide it completely in 
order to allow it to retract, that the blood may be stopped, for, 
as shall be afterwards shewn, it is improper to attempt to do this 
by compression alone. The canal of the artery becomes, there- 
fore, by the operation of arteriotomy, completely obliterated, 
and as the circulation is afterwards carried on by a greater or less 
number of enlarged branches, neither the original trunk nor a 
branch of sufficient caliber will be found in the temporal region, 
on which the operation of arteriotomy could be repeated, should 
such a measure be deemed necessary. 
Lancet . 
