PATHOLOGY: W. S. HALS TED 
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pain of cervical rib rarely make wide excursion movements of the arm. (b) 
The degree of occlusion is constant in the experimentally constricted vessel. 
When an arterial trunk is ligated it becomes occluded to the first proximal 
and first distal branches and ultimately reduced to a fibrous strand. 
From observations which we have made on man and dogs I am quite sure 
that there may be a remarkable fall in blood pressure in what I have termed 
'the dead arterial pocket,' while there is still little if any sign of diminution 
in the caliber of this portion of the vessel. For example, the right common 
carotid was ligated by the writer in a case of aneurysm of the external carotid. 
About 3 months later, in the course of an operation for the excision of the un- 
cured aneurysm, the internal carotid, dead-pocketed between the circle of Willis 
and the, carotid ventricle, was freely exposed for a considerable distance. It 
had lost its cylindrical form, being flat and tape-like, and, although evi- 
dently possessing a considerable lumen, seemed to be empty. When incised, 
a few drops of blood oozed without pulse from the little cut. The artery was 
then resected. Its wall was thickened on one side but the lumen was still 
perhaps three times that of a radial artery. Similar observations I have made 
twice on the external iliac of the dog after occlusion of this vessel at its origin 
from the aorta. In the dead pocket between the aorta and the origin of the 
circumflex iliac and common trunk of the epigastric and obturator arteries 
the blood pressure must have been almost nil, because from a little slit in the 
apparently normal arterial wall of the relatively empty external iliac artery the 
blood escaped very slowly in a tiny, almost pulseless jet about 1 cm. high; 
whereas, from the femoral artery, below the profunda, the blood spurted nor- 
mally from a similar knife-prick. 
Hence in an artery doomed to obliteration, it would seem that the blood 
pressure may be lowered before the occlusion process sets in — the lowered 
pressure being, perhaps, the immediate factor leading to the obliteration. 
Can these observations have any bearing upon the explanation of the dila- 
tion of the aorta above its trifurcation and of its triad branches in the dog 
after partial occlusion; of the dilation of the carotid in the human subject 
which I have observed in one case after partial occlusion of the innominate 
combined with ligature of the first and third portions of the right subclavian; and 
of the aneurysm of the third portion of the subclavian in cases of cervical rib? 
In 1906 Dr. Richardson and I made the observation that after partial oc- 
clusion of the thoracic aorta the maximum pressure may be permanently 
lowered and the minimum pressure permanently increased distal to the con- 
stricting band; and in recent experiments Dr. Reid and I have observed that 
after constriction of the lower abdominal aorta the diastolic pressure may be 
so increased and the systolic pressure so lowered as to reduce the pulse pressure 
by nearly one half. The blood stream in this case, passing with greater veloc- 
ity and less pressure through the band prevents the obliteration of the artery 
to the nearest branch, the pocket being not a dead one as it is in the case of 
