204 
PATHOLOGY: W. S. HALSTED 
than in the Pacific ocean. The recent date and the rapid rate of subsidence 
appear to be of greater importance than its amount in the case of the Great 
Chagos bank, where the submergence does not seem great enough to drown 
the reef-building corals. Here the muddy central area is 40 or 50 fathoms 
deep; it is bordered by an irregular sandy bank from one to 5 miles or more in 
breadth and from 15 to 20 fathoms in depth, on the outer margin of which 
rises a rim about a mile in width, and only 5 or 10 fathoms in depth; singularly 
enough, there is little living coral on the outer rim, though knobs of growing 
coral rise from the central depression. The diameters of the whole mass range 
from 50 to 75 miles: its form suggests that a prolonged stationary period, 
during which a broad atoll-reef was developed, was followed by a subsidence of 
about 10 fathoms, after which a shorter stationary period permitted, the up- 
growth of a narrower reef; then a rapid and presumably recent subsidence 
of 5 or more fathoms ensued, since which no effective reef growth has taken 
place, possibly because, according to Daly's suggestion, the submerged corals 
were smothered by wave- and current-shifted sediments. 
Unfortunately no archipelagoes comparable to those of the Australasian 
region are present in the Indian ocean to give evidence in the case, but it may 
be noted that a few high islands which occur in association with the Indian 
ocean banks — chiefly the granitic islands in the area of the great Seychelles 
bank — have narrow and unconformable fringing reefs on their deeply eroded 
and well embayed shores; thus they repeat in a small way the more abundant 
and therefore more compulsory evidence that is provided by the charts of the 
Philippines. Further details on these topics are given in an article on "Sub- 
marine Banks and the Coral Reef Problem," now in course of publication in the 
Journal of Geology, and in an article on the "Subsidence of Reef-encircled 
Islands," soon to appear in the Bulletin of the Geological Society of America. 
DILATION OF THE GREAT ARTERIES DISTAL TO PARTIALLY 
OCCLUDING BANDS 
By William S. Halsted 
Medical School, Johns Hopkins University 
Read before the Academy, April 22, 1918 
The incentive to the work was primarily the desire to cure aneurysms of the 
abdominal aorta and common iliac arteries. 
The method usually employed for the cure of aneurysm is the simplest, viz., 
the ligation of the affected artery proximal and as close as feasible to the 
aneurysm. The aorta has been ligated 25 or more times in man, and always 
with fatal result. Death has been due to hemorrhage or overtaxed heart. 
Neither gangrene nor paraphlegia has ever resulted from ligation of the aorta 
