194 Report on the Fafholof/ical Anatomy of Fleuro-pneumonia. 
completely fills them with a tight adherent plug. When any 
vessel is quite occluded, all its branches are found filled with clots 
of blood, which are often black and soft, evidently being of 
recent formation. When an extensive plug lies in a large artery 
without causing its occlusion, many of its minute branches are 
usually quite stopped. This appears sometimes to depend on 
small emboli, formed by fragments broken off the thrombus in 
the parent trunk of the artery. In other cases a number of small 
vessels throughout the diseased part may be choked up with 
thrombi, which have evidently been formed primarily in them, 
and which seem to be caused by several points of the intima 
being damaged. Once a branch of a vessel has been filled, the 
clot seems to grow with great rapidity into the larger branches, 
so as to produce occlusion of the parent trunk and of the neigh- 
bouring branches arising from it. 
As may be inferred from what has already been said of the 
haemorrhagic consolidation, the parts of the lung parenchyma 
to which the plugged vessels lead,- are those thus suddenly en- 
gorged. The various appearances met with in the formation of 
haemorrhagic infarction are now well understood, so I need not 
pause here to explain them.* Here the infarction is well marked, 
but, owing to the many variations in the method in which the 
coagulation in the vessels may be brought about, there is a much 
greater variety in its form than is commonly met with in those 
cases where it depends exclusively upon embolic plugging. 
The constant conical shape of the black consolidation can now 
be easily explained, as well as the suddenness with which the 
engorgement occurs. The variegated appearance produced by 
small dark-red patches, which is now and then seen on the cut 
surface, obviously depends upon small scattered infarcts, which 
result from numerous emboli, or from irregular and diffused 
injury to the intima of the small vessels. 
* This form of engorgement and liaamorrbage, caller! by Laennec 'pulmonary 
apoplexy, is now nnivcrsally admitted to dei^end on a local impediment to the 
circulation, such as an embolus impacted in an artery. There being no arterial 
anastomosis in tin; lung, such a plug has a very marked effect. The embolus 
cuts off the normal sujjply of Ijlood from the part, and the pressure in the arterial 
branches beyond the stoppage falls to zero. The blood, however, eau»still find 
its way through the capillaries into the branches at the di.slal side of the ])lug. The 
brandies of the occluded artery are tlius reduced to tlio condition of occluded 
Veins, and as tliey have none but capillary connections, they may be said to form 
blind ends to the adjacent arteries. The blood then trickles into these arterial 
branches and lills them, but no onward flow can take jilaco, therefore they become 
intensely engorged with stagnant blood. Under these circumstances the inner 
coat of the vessels is deprived of its nutrition, for which the constant renewal of 
the blood is required. This starvation of the minute vessels renders them unfit 
for their function ; they lose thiiir ])ower of retaining the blood, which escapes 
into the neighbouring textures, ibrming the deuso black consolidation now known 
U8 hxmorrluKjic infarction. 
