432 
COAGULATION OF THE BLOOD. 
seat of the wound as tightly as he possibly could. It had 
been in this condition with the bandage thus applied for 
forty-eight hours when I reached the patient, and the limb 
had all the appearance of being dead. It was perfectly cold, 
and any colour which it had was of a livid tint. But 
having been lately engaged in some of the experiments 
which I have been describing, and having thus become much 
impressed with the persistent vitality of the tissues and the 
concomitant fluidity of the blood, I determined to give the 
limb a chance by tying the brachial artery. Before I left the 
patient’s house he had already a pulse at the wrist, and I 
afterwards had the satisfaction of hearing that the arm had 
proved a useful one. 
One of the two arguments in favour of activity on the 
part of the vessels as a cause of fluidity of the blood having 
been completely disposed of, let us now consider the other 
—viz., the rapid coagulation of blood shed into a basin, 
appearing at first sight to imply a spontaneous tendency of 
the blood to coagulate, such as would have to be counteracted 
by the vessels. This, also, has proved fallacious. 
In the first place, it appears that the coagulation, after all, 
does not go on in a basin so suddenly as one would at first 
sight suppose, but always commences in contact with the 
foreign solid. When blood has been shed into a glass jar, if, 
on the first appearance of a film at the surface, you introduce 
a mounted needle, curved at the end, between the blood and 
the side of the glass, and make a slight rotatory movement 
of the handle, you see through the glass the point of the 
needle detaching a layer of clot, whatever part you may 
examine. The process of coagulation having thus com¬ 
menced in contact with the surface of the vessel into which 
the blood is shed, may, under favorable circumstances, be 
ascertained to travel inwards like advancing crystallization 
towards the centre of the mass. It appears, however, that 
this extension of the coagulating process would not take 
place had not the blood been prepared for the change by 
contact, during the process of shedding, with the injured 
orifice of the blood-vessel and with the surface of the receptacle. 
I have only very recently become acquainted with the remark¬ 
able subtlety of the influence exerted upon blood by ordinary 
solids. I was long since struck with the fact, that if I intro¬ 
duced the point of an ordinary sewing-needle through the 
wall of a vein in a sheep^s foot, and left it for twelve hours 
undisturbed, the clot was still confined to a crust round the 
point of the needle, implying that coagulum has only a very 
limited power of extension. I thought, therefore, that by 
