CHAPTER XXXIV 

 SHOCK 



Shock may be due to a variety of causes. In general it may be de- 

 scribed as a condition in which there is more or less paralysis of the 

 sensory and motor portions of the reflex arc, along with profound dis- 

 turbances in the circulatory system, subnormal temperature, and fre- 

 quent and shallow respiration. Certain of the symptoms may be consid- 

 ered as primary and others as secondary, an important step in the in- 

 vestigation of this difficult and important problem being to distinguish 

 between the two groups. Before attempting to do this, however, it will 

 be profitable to differentiate as sharply as possible the various conditions 

 in which one or another of the many varieties of shock is liable to occur. 



Several varieties of shock have been described but it is particularly 

 that known as surgical or secondary shock that is important. The less 

 important varieties are as follows: 



1. Gravity Shock. This is caused by the stagnation of blood in the splanchnic ves- 

 sels and the consequent inadequate filling of the heart in diastole. It occurs, when the 

 erect position is assumed, in animals in which the mechanism which ordinarily compen- 

 sates for the tendency of gravity to make the blood flow to the dependent parts is 

 inadequate. Thus, when a domesticated rabbit with a large pendulous abdomen is 

 held in the vertical tail-down position for any length of time, the animal gradually 

 passes into a shocked condition and may die in a short time (20 to 30 minutes). Ob- 

 servation of the blood vessels of the ear or a record of arterial blood pressure will 

 show that the cause of shock in this case has been a great curtailment of the blood 

 supply to the upper part of the body, and therefore to the nerve centers. The shock 

 is entirely dependent upon the laxity of the abdominal musculature, for if a binder 

 is applied to the abdomen, or if the experiment is performed on a rabbit whose 

 abdominal musculature is in good condition, gravity shock does not develop. Nor can 

 fatal gravity shock be produced in a dog, although in a deeply anesthetized animal 

 a marked fall in arterial blood pressure occurs when the vertical toil-down position is 

 assumed. In man, in whom compensation for the erect posture is highly developed, 

 shock from gravity occurs only when there has been some other considerable upset in 

 the circulatory mechanism (see also page 249). 



2. Hemorrhagic Shock. Free hemorrhage produces a typical condition of shock, but 

 the extent to which different individuals react to the same degree of hemorrhage 

 varies considerably. The essential factor in the production of hemorrhagic shock is 

 of course similar to that of gravity shock namely, a deficient diastolic filling of the 

 heart with blood. Details concerning the effect of hemorrhage will be found elsewhere 

 (page 138). 



In man hemorrhagic shock is often indistinguishable from surgical shock. This does 



301 



