The low blood pressure with which I am concerned in this paper is that which during and since the recent war has been recognized as "secondary shock." In contrast with this is the condition that has been termed "primary shock" or "collapse." A satisfactory explanation for the latter condition seems to have been offered by Goltz,1 in 1863, when he found that a blow on the exposed mesentery of the suspended frog caused reflex inhibition of the heart through the vagus and a lessening of vascular tone generally throughout the body and especially in the abdominal cavity. As regards "secondary shock," many suggestions have been presented to account for the low blood pressure and other phenomena. The older ideas are enumerated in Groeningen's treatise,2 while the more recent ones are described in detail in Cannon's monograph.3 Of the theories that have been advanced as to the cause