ARTERIOVENUS FISTULAS An Arterviovenus Fistula as a Stimulus to the Development of a Collateral Circulation. —The presence of an arteriovenous fistula constitutes a most powerful stimulus to the development of a collateral circulation. This point, I think, has not been sufficiently stressed. Matas,1in advising against too early operations on patients with arteriovenous aneurysms, speaks of the advantage of waiting for the development of a collateral circulation, and he advises encouraging this development by the compression of the proximal artery as advocated by Bramann,2Kikuzi,3Siago and others. La Roque4believes that the collateral circulation becomes impaired in the presence of an arteriovenous fistula. A study of our own cases, as well as of many carefully reported cases in the literature, and the result of our experimental work leave no doubt that an abundant collateral circulation develops around an arteriovenous fistula, greater even than the collateral