ON THE EARLY STAGES OF INFLAMMATION 245 
so that the vein may be vertical in position, the upper part of the venous com- 
partment included between the ligatures will within a very few minutes become 
colourless in consequence of rapid subsidence of the red corpuscles, implying 
that they are already closely aggregated, although, if the skin be carefully 
replaced so as to prevent drying of the tissues, the blood will remain fluid in 
that part of the vein for many hours. Whether the adhesiveness of the cor- 
puscles in this case depend on a post mortem change in the vessels, or whether 
it is merely the result of the large size of the vein preventing the tissues from 
acting effectually on the blood, remains to be determined; but such a fact 
seems to prove that a higher grade of vital activity, so to speak, is required 
to prevent adhesiveness of corpuscles than to maintain the fluidity of the blood. 
Hence it is probable that, even if the blood were at rest in the vessels of a part, 
a stronger degree of irritation would be required in order to determine coagula- 
tion than would suffice to induce adhesiveness of the corpuscles, which seems 
to be a more sensitive test of a deviation of the tissues from the standard of 
health. I have, however, ascertained, by experiments upon the amputated 
sheep’s foot, that if caustic ammonia is applied freely to a part of a vein after 
pressing the blood out of it, and the blood allowed to return when the ammoniacal 
odour has passed off, coagulation takes place in the portion of the vessel which 
has been so treated, although the chemical action of ammonia, if any of it 
remained in the tissues, would tend to prevent or check coagulation.t. I have 
also found a similar local clot form, though more slowly, after merely pinching 
a piece of a vein. 
The principal results obtained in this section may be summed up as 
follows :— 
The effects produced upon the circulation by the application of an irritant 
to a vascular part are twofold, consequent upon two primary changes in the 
tissues, which, though often concomitant, are entirely independent both in 
nature and mode of production. One of these is dilatation of the arteries 
(commonly preceded by a brief period of contraction), giving rise, in proportion 
to the increase of calibre, to more free flow through the capillaries, the blood 
remaining unaffected, except in the rate of its progress. This purely functional 
phenomenon is developed indirectly through the medium of the nervous system, 
being not limited to the part acted on by the irritant, but implicating a sur- 
rounding area of greater or less extent. The other change is the result of the 
direct operation of the irritating agent upon the tissues, which experience some 
alteration, in consequence of which the blood in their vicinity becomes impaired, 
losing the properties which characterize it while within a healthy part, and 
* See the paper ‘On Spontaneous Gangrene’, &c., before referred to. 
