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PATHOLOGY: W. S. HALSTED 
total obliteration. The blood in this pocket beyond the constriction streams, 
presumably, in whirlpools, somewhat as in the vein and, also, as in the artery 
in arterio-venous fistula; the thrill, not palpable at first if the occlusion has 
been nearly complete, later may be perceived with the finger; and the bruit, 
always audible with the stethoscope, becomes louder as the peripheral arterial 
resistance increases. 
To these factors, then — to the abnormal play of the blood in the relatively, 
as distinguished from the absolutely dead pocket and to the absence of normal 
pulse pressure, essential probably to the maintenance of the integrity of the 
arterial wall, we may have to look for the solution of our problem. 
We have completely occluded the aorta just above the trifurcation only in 
dogs. Usually there has been no distal dilation, and in a previous paper I 
made the statement that dilation had not been observed below a totally oc- 
cluding band. Since then, however, a slight degree of dilation, distal to the 
completely obturated vessel, has taken place in three instances. A dilation of 
this ventricle-like portion of the aorta between the band and the trifurcation 
might be expected even in case of complete occlusion, for the anastomosis is 
very free in this situation and the dead pocket is usually, and perhaps always 
too short to become obliterated. Lumbar branches may be given off just below, 
as they are just above the band. 
In two instances I have made the following observation in testing, during 
the life of the animal, for the patency of the aorta under the band. Pressure 
with the finger immediately above the band shut off the pulse in what we term 
the ventricle; whereas, pressure with the back of the scalpel-blade, made as 
close to the band as possible, did not. In these cases there was a patent lum- 
bar artery so close to the proximal edge of the band that pressure by the 
finger obliterated it, whereas, the knife blade which could be brought to bear 
on the aortic wall between this little artery and the upper edge of the band did 
not interrupt the flow in this important asastomotic branch. The contribu- 
tion of this little artery to the anastomotic bloodstream was sufficient to con- 
vert an impalpable into a palpable pulse. A palpable pulse in the ventricle 
below the band is so invariable, whether the aorta has been completely oc- 
cluded or not, that the patency of the artery under the band cannot be defi- 
nitely determined during the life of the animal unless temporary occlusion of 
it between the band and the nearest lumbar artery obliterates or decidedly 
influences the pulse in the ventricle. If pressure above the band does not 
affect the pulse just below it we may conclude that obturation is complete. 
Fortunately it occurred to me a few days ago to restudy, with reference to 
the possibility of finding depicted a dilation of an artery below a ligature, the 
sketches of surgeons who in bygone years had experimentally ligated the blood- 
vessels of animals. I was delightfully surprised to find, in the beautifully 
illustrated volume of Luigi Porta 1 published in 1845 two drawings which por- 
trayed a pronounced dilation of the aorta and its ventricle immediately below 
