STUDIES ON THE CIRCULATION IN MAN : XII. A STUDY OF INEQUALITIES IN THE BLOOD FLOW IN THE TWO HANDS (OR FEET) DUE TO MECHANICAL CAUSES (EMBOLISM, COMPRESSION OF VESSELS, ETC.) OR TO FUNCTIONAL (VASOMOTOR) CAUSES, WITH A DISCUSSION OF THE CRITERIA BY WHICH THE CONDITIONS ARE DISCRIMINATED.

1. In cases in which great inequalities in the blood flow in the two hands were produced by mechanical causes (ligation or compression of vessels, embolism), the stability of the ratio of the flows, in successive measurements at short intervals, was found to be characteristic. Over long intervals the opening up of collateral circulation or the progressive increase of the block (in a case of multiple embolism with thrombosis) was followed by changes in the ratio of the blood flows in the normal and the affected part. Another criterion of these conditions was found to be that the inequality was not abolished by producing general vasomotor changes; e. g., by altering the external temperature. 2. In certain cases inequalities in the blood flow in the two hands (or feet) were found which were not stable from day to day, and which could be abolished, reduced, increased, or reversed by alterations in the external conditions which bring about general vasomotor changes. These inequalities, not associated with clinically recognizable differences between the parts compared, were interpreted as due to unequal activity of the vasomotor mechanism on the two sides. The condition appeared to be most frequent in certain groups of neurological cases.