288 THE CIRCULATION OF THE BLOOD 



2. Hemorrhagic Shock. Free hemorrhage produces a typical condi- 

 tion 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 grav- 

 ity shock namely, a deficient diastolic filling t)f the heart with blood. 

 Details concerning the effect of hemorrhage will be found elsewhere 

 (page 135). 



3. Anesthetic Shock. So far as blood-pressure reflexes are concerned, 

 an animal can be kept in a perfect condition when ether is administered 

 in just sufficient amount to produce light anesthesia. When larger 

 quantities of ether are employed, a typical condition of shock is almost 

 certain to supervene after a time. In such instances the arterial blood 

 pressure remains low and can not be restored even after an hour or two 

 of artificial respiration. There is, however, a difference between ether 

 shock and the variety which we shall discuss later under the title of 

 surgical shock : in the former, removal of the anesthetic causes all reflexes to 

 return, whereas in surgical shock most of these are subnormal. The danger 

 of anesthetic shock has been considerably diminished in the clinic by 

 the more careful administration of ether or by the use of other anesthet- 

 ics, such as nitrous oxide gas. A condition closely simulating shock 

 may also be induced in the earlier stages of the administration of anes- 

 thetics when these are badly given, but paralysis of the heart or of the 

 respiratory center is a usual contributory cause. 



4. Spinal Shock. Spinal shock is produced by section of the spinal 

 cord, but it is to be carefully distinguished from all other forms of shock 

 because of its local character, as it affects only those parts of the body 

 which lie below the level of the lesion in the cord. Above this level the 

 animal may be in a perfectly normal condition, except in cases where 

 the section has been at so high a level that it has severed the vasocon- 

 strictor pathway and thereby produced a fall in blood pressure from 

 vasodilatation. Even when this has happened the part of the animal 

 anterior to the spinal lesion is by no means in a condition of shock. Thus, 

 Sherrington observed in a monkey whose spinal cord had been cut far 

 forward that, although the posterior part of the body was in profound 

 spinal shock and the blood pressure very low, the animal amused him- 

 self by catching flies with his hands. A sufficient description of the con- 

 dition of spinal shock has been given elsewhere, but here it may be noted 

 that it consists essentially in a paralysis involving at first all of the re- 

 flex mechanisms, including the control of the sphincters, in the part of 

 the cord posterior to the section. In the course of a few days or weeks, 

 according to the position of the animal in the scale of development, the 

 reflexes gradually return, until ultimately in a couple of months in a 



