242 ON THE EARLY STAGES OF INFLAMMATION 
the particles of the fibrine, such as is not exercised by the walls of the vessels ; 
or, in other words, that the vascular parietes differ from all ordinary solid sub- 
stances in being destitute of attraction for that element of the liquor sanguinis. 
The blood-vessels are not the only constituents of the animal body which 
have these remarkable relations to the blood. If the integument of a sheep’s 
foot be partially reflected, and one of the subcutaneous veins immediately 
wounded, so as to let some blood run into the angle between the skin and the 
rest of the limb, before any drying of the tissues has occurred, care being taken 
that no hairs or other solid matters have been introduced, this blood will remain 
in whole or in part fluid for half an hour or more ; whereas, if blood from the same 
vessel be placed in contact with any ordinary solid, whether on the foot or else- 
where, it will coagulate in perhaps five minutes.' This is sufficient proof that 
the subcutaneous cellular tissue resembles the lining membrane of the vessels 
in its conduct towards the blood. The long time during which blood has been 
observed to remain fluid but coagulable in the tunica vaginalis, seems to show 
that serous membranes are similarly circumstanced: and it appears probable 
that the same may be the case with other tissues. fp 
But though some of the facts above mentioned furnish clear evidence that 
ordinary solid matter induces coagulation by an attractive agency, it by no 
means follows that the tissues are necessarily merely neutral in their conduct 
towards the blood in this matter. It is quite possible that they may exert 
an active influence upon it, in consequence of which the particles of fibrine 
may experience a mutual repulsion, in the same way as would seem to be the 
case with the pigment-granules of the chromatophorous cells of the frog during 
the process of diffusion,? Indeed some such hypothesis seems almost necessary 
having occurred in the interval. This circumstance seems to prove that the ammonia is free in the 
blood in its normal condition within the vessels, and not merely liberated during the process of coagu- 
lation ; for it is to be remembered that the mere wounding of a vein in no way interferes with the fluidity 
of the blood in it, except at the wound. 
* After the blood has lain for some time in the angle between the skin and the limb, it coagulates, 
if removed from it, much more rapidly than blood freshly shed,from a vessel. Thus, in one case, blood let 
out from a vein was part of it placed at once on a glass plate, and part allowed to run into the angle 
between the skin and limb. That on the glass plate was not completely coagulated for ten minutes ; 
but that in the other situation, having been left for twenty minutes, and then transferred to the plate, 
was a consistent clot within six seconds, indeed as soon as I could examine it. This fact seems to me 
to throw great light upon the subject of coagulation. The sudden transition from perfect fluidity to 
a coagulum can only be explained, I conceive, on the hypothesis that the ammonia had almost all escaped 
while the blood lay in the angle ; yet this escape had not caused coagulation. Hence it seems to follow, 
that ammonia is in no way essential to the fluidity of the blood while it is surrounded by healthy tissues. 
Another point, which the simple experiments upon the sheep’s foot show clearly, is that a certain amount 
of ammonia in the blood will retard without preventing the deposit of fibrine upon a needle or other 
ordinary solid introduced into the vessels; and it appears very doubtful whether healthy blood ever 
contains sufficient ammonia to prevent such an occurrence. 
* See p. 56 of this volume. 
