Morphine alone, or in combination with ether as a general anesthetic, reduces susceptibility to shock, and appears to be an equalizer of pressure and a tranquillizer of an excited heart. Nitroglycerin and the nitrites usually fail to raise or even sustain pressure. _Saline infusion_ and _adrenalin_ are the _reliable and efficient means_ to be used in combating shock and collapse; _they always raise blood pressure_, and the latter is the most powerful of all known vasomotor constrictors. Adrenalin always produces rise of blood pressure, even after cocainization of the medulla and cord or destruction of the medulla, division of the splanchnics, or arrest of the heart by powerful electrical currents (2300 volts, alternating). Even after death by decapitation and an interval of fifteen minutes, adrenalin salt solution thrown into the veins causes a rise of blood pressure. If this be combined with artificial respiration and rhythmic pressure over the heart, resuscitation is possible in most extreme cases. In one case, reported by Crile, a human heart which had stopped beating for nine minutes was made to resume its pulsation for thirty-two minutes. From all this it will appear that the heart stimulants, so called, have a very limited applicability. Crile further experimented by raising the atmospheric pressure surrounding the animal, and found that blood pressure was somewhat exalted. The reverse was also found to be true. When he so arranged his experiment that an animal inhaled air under increased pressure he found the tendency was rather to impairment of heart action, blocking the circulation and reducing pressure. Changing the experiment and causing the animal to breathe air at normal pressure while the body was under increased atmospheric pressure, blood pressure was notably raised, but respiration became labored and the heart’s action impaired. After death the heart and the pulmonary vessels were found engorged. This has its practical interest because it concerns not alone the general treatment of shock, but the management of those cases where the thorax must be opened, as in the surgery of the heart, the lungs, the esophagus, etc., and the mechanical devices recently suggested for maintaining differences of atmospheric pressure, and preventing a traumatic collapse of the lungs.