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Beside the previously described changes in capillary resistance occurring after a period of latency and lasting for several days or weeks, another type of response was found in both human subjects and experimental animals which sets in promptly and wears off within 4 hours. It is suggested that this be termed ‘immediate capillary stress response’ for the sake of distinction from the ‘late capillary response.’ Both immediate and late responses may show patterns of increase, decrease and biphasic reaction or there may be upon the same stress no change in the capillary resistance at all. Since the immediate capillary stress response, in contrast to the late response, appears in the adrenalectomized animal as well as in the intact animal, it is postulated not to be dependent on the adrenal cortex.

Role of the thymus in the alarm reaction was investigated on albino rats by studying the capillary resistance and the capillary stress response after thymectomy. Control animals were of the same breed, weight and sex and they matched the thymectomized rats also in that they were exposed to the same surgical trauma (sham thymectomy). No difference was found between thymectomized and control animals as far as general development, weight, maturation, life span, resistance to infections or capacity to endure stressful situations were concerned. The capillary resistance level did not change in these two groups of rats during an observation period of 3–10 months. Typical capillary response was found to most varied forms of stress in the thymectomized as well as in the sham operated animals. Adrenalectomy in the thymectomized rats resulted in capillary resistance changes similar to those in the sham operated or intact controls. Adrenalectomy abolished the late response but did not interfere with the immediate response in the presence as well as in the absence of the thymus. The conclusion is warranted that the thymus does not influence capillary resistance or the capillary stress response. No proof was forthcoming in these experiments in favor of a specific role of the thymus in the alarm reaction.

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