From a historical point of view the first studies on the response of the organism to stressful situations in general, and on the psychobiology of stress in particular, are probably those of Cannon and de la Paz, the physiologists who showed in 1911 that the adrenal medulla and the sympathetic system are involved in emergency situations. Cannon noted that the venous blood of cats frightened by barking dogs contained adrenaline, a response of the organism which was prevented by adrenalectomy or by section of the splanchnic nerve innervating the adrenal medulla. Cannon suggested that the adrenal...