CHAPTER XXXIII 

 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, frequent 

 and shallow respiration, and more or less unconsciousness. Certain of 

 these symptoms may be considered as primary and others as secondary, 

 an important step in the investigation of this difficult and important 

 problem being to distinguish between the two groups. Before attempt- 

 ing 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 said to occur. 



The following varieties of shock have been described: 



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

 splanchnic vessels 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 compensates 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). Observation 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 (Fig. 244). The 

 shock is entirely dependent upon the laxity of the abdominal muscula- 

 ture, for if a binder is applied to the abdomen, or if the experiment is 

 performed on a rabbit whose abdominal musculature is in good condi- 

 tion, 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 x the vertical tail- 

 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 245). 



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