SHOCK 293 



heart. The consequent curtailment in the systolic discharge does not, 

 however, at first cause any marked fall of arterial blood pressure be- 

 cause of a reciprocal constriction of the peripheral arterioles of the 

 body. Meanwhile, however, the stagnation of blood in the capillary areas is 

 progressively increasing, so that less and less blood remains available 

 for the systemic circulation. Consequently, after a while, in spite of 

 the arterial constriction, the blood pressure falls to the dangerous shock 

 level, and the secondary symptoms of fall in temperature, dulling of the 

 reflexes, etc., supervene. Increasing viscidity of the blood also retards 

 its flow. 



The fundamental question in the pathogenesis of shock concerns there- 

 fore the cause of the stagnation of circulatory fluid in the capillaries and 

 venules. Two hypotheses have been offered, one being that the stimulation 

 of afferent nerve fibers to the respiratory center causes excessive alveolar 

 ventilation with a consequent washing out of carbon dioxide from the 

 blood (acapnia), which causes a veno-capillary atonia, and the other, 

 that a bombardment of the vasoconstrictor and other nerve centers 

 by afferent impulses brings these centers into a condition of exhaus- 

 tion, which is the essential cause of shock. The acapnia hypoth- 

 esis may be at once dismissed, since, on the one hand, it has been 

 shown that in typical shock there is no deficiency of carbon dioxide in 

 the venous blood (Short), 33 and on the other hand, conditions of shock 

 are often produced without excessive breathing. 



Nor is there any evidence to support the view that shock is caused by 

 fatigue of the cardinal centers as a result of excessive sensory stimu- 

 lation. In the first place, it has been shown by Mann 34 that during han- 

 dling of the abdominal viscera the nervous impulses transmitted up the 

 spinal cord are much less marked than those transmitted when the cen- 

 tral ends of sensory nerves are stimulated by operative processes on the 

 limbs and joints, although shock is much more readily produced by the 

 former procedure. The method employed by Mann for detecting the 

 existence of these afferent impulses was that of Forbes and Miller, in 

 which electrodes are placed on the brain stem in decerebrate animals, 

 and the current of action which accompanies the passage of nerve im- 

 pulses registered by a string galvanometer. Although this method is 

 simple and direct in principle, it has been found by Mann to require 

 great care in practice because of the fact that the slightest movement 

 of the head end of the animal produces deflections of the galvanometer. 

 If the further results of this investigation should show, as the early 

 ones have done, that shock may be produced in an animal without any 

 observed deflection of the galvanometer, it will disprove once and for all 



