PATHOLOGY: W. S. HALSTED 
209 
the site of ligation. The ligatures in the two dogs had been applied eight and 
fifteen months before the death of the animals. There is a great bundle of 
dilated vessels — the vasa vasis — bridging the gap between the retracted ends 
of the divided aorta. 
Thus three-quarters of a century ago this great, perhaps the greatest sur- 
geon of Italy, furnished irrefutable proof of a remarkable phenomenon which 
must eventually have interest for the physiologist, the pathologist and the 
surgeon. Luigi Porta describes the drawing but makes no further comment 
upon the dilation. 
Before the introduction of antiseptic surgery by Lister, thrombosis quite 
invariably followed ligation of an artery, and it was to the organization of the 
thrombus that the surgeon looked for the prevention of secondary hemorrhage 
and for the preservation of the life of the patient. If thrombi formed in these 
two cases of Porta they must have been eventually absorbed, for the distribu- 
tion of the dilated vasa vasis proves that the aortic free ends were patulous, and 
we have further proof of this in the dilation of the aortic ventricle just below 
the site of the ligation. 
In the course of my experiments in partial occlusion of the arteries I have 
often studied the illustrations, carefully I thought, in Luigi Porta's work, but 
not until I scanned them with the particular object in view did I discover the 
dilations so strikingly manifest. I wonder if anyone has ever commented upon 
or been interested in these two observations of Porca. 
In the human subject I have in one instance observed a remarkable dilation 
of an artery distal to a partially occluding band. In this case an aluminum 
band was applied to the innominate artery for the cure of a subclavian 
aneurysm. A few weeks later, the aneurysm being uninfluenced by this 
procedure, the subclavian artery was ligated both proximal and distal to the 
sac, and a cure effected. Three years later a quite cylindrical dilation of the 
right common carotid was observed; and now, twelve years after the application 
of the band, the common carotid artery is strikingly dilated throughout its 
entire length. The band on the innominate can be palpated; the blood is 
coursing through it, and distal to the band is a distinct bruit (exhibit). 
Summary. — 1. A partially occluded artery (abdominal aorta, innominate, 
carotid, subclavian) may dilate distal to the site of constriction. 
2. The dilation is circumscribed and has been greatest when the lumen of 
the artery (the aorta) was reduced to one-third or perhaps one-fourth of its 
original size. 
3. When the obturation has been slight in amount dilation has not been 
observed; of 7 cases of complete obstruction there was a very moderate degree 
of dilation in 3, and none in 4. 
4. Complete or partial occlusion of the thoracic aorta may be followed by 
dilation central to the point of constriction. 
5. Dilation or aneurysm of the subclavian artery has been observed twenty- 
seven or more times in cases of cervical rib. 
