The development of the collateral circulation after ligation of the innominate and right common carotid arteries for subclavian aneurysm was studied in two cases by measuring the rate of blood flow in the hand's from time to time.

In a woman, sixty-eight years old, the flow in the right hand three weeks after the operation was two-sevenths of that in the left. Nineteen weeks after the operation the flow in the right hand was more than three-fourths of that in the left, although no pulse returned until long afterwards.

In a man, twenty-five years old, the flow in the right hand eleven days after the operation was between one-fourth and one-fifth of that in the left. Seventeen days after the operation the flow in the right hand was nearly one-third of the flow in the left. Twenty-four days after the operation the flow in the right hand had increased to more than one-half of the left hand flow. Thirty-one days after the operation the flow in the right hand was three-fifths of that in the left, without return, as yet, of any pulsation.

Before the operation the flow in the right hand was markedly greater than in the left, notwithstanding the small size of the right radial pulse as compared with the left. The explanation of this fact is discussed.

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