THIs paper is concerned with the rather large changes in the general blood pressure which we observed in man during the muscular exercise of a limb when the circulation of blood through its working muscles was arrested by mechanical pressure. Our earliest observations were made in the course of experiments which were not concerned directly with the present investigation.METHOD Special large sphygmomanometer cuffs were placed round the thighs of a normal subject who was in the sitting posture, and a flat iron weight of 12 kg. was laid across the knees. During the control period the systolic and diastolic blood pressures were measured in an arm by the auscultatory method at about half-minute intervals, until constant readings were obtained. The sphygmomanometer cuffs round the thighs were then inflated rapidly to a pressure well above the subject's systolic blood pressure in order to arrest the circulation through both the legs and further blood pressure readings were taken in the arm. The subject was next instructed to raise and lower the knees. The distance traversed by the weight during each of its excursions was about 5 cm. The movement was performed using as far as possible only the calf muscles. This movement was repeated at intervals varying in the different experiments between 05 and 2 sec. The first experiment of a series on any one subject was usually only for the training of the subject and the results then were not recorded.

IN a previous paper [Alam & Smirk, 1937] it was shown that a blood pressure-raising reflex may be demonstrated in normal human subjects which takes its origin from the voluntary muscles and is concerned in the rise of the general blood pressure during muscular exercise. This blood pressure-raising reflex from the voluntary muscle depends on an accumulation of metabolites in the muscle and is elicited by local muscular exercise of a forearm or a leg, provided that the rate of performance of the exercise is sufficiently great to cause such accumulation of metabolites. The reflex is elicited also when the local muscular exercise is performed at a slow rate but with the circulation through the exercising part of the limb arrested either by plunging the limb vertically into a deep bath of mercury or by inflating a sphygmomanometer cuff, placed round the proximal part of the limb, to well above the systolic blood pressure. The striking feature of this blood pressure increase, and showing clearly its reflex origin, is that (in the absence of further exercise) the blood pressure may be maintained at a high level for periods of at least half an hour by maintaining the arrest of the circulation through the exercised muscles and thus preventing the removal of the accumulated metabolites by the blood stream.The degree of increase in the general blood pressure produced by this reflex is, under equal conditions, about the same for any given subject, but the degree of increase varies greatly from one subject to another.Thus, in normal man, the maximal increases in systolic pressure which we have been able to secure by this method have varied between 10 and 90 mm. of mercury.In the present paper a study will be made of another reflex effect of the accumulation of the metabolites of muscular exercise in the leg muscles, namely, increase of the pulse rate.

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