302 THE CIRCULATION OF THE BLOOD 



not mean that every case of severe hemorrhage is necessarily also suffering from the 

 condition usually understood as surgical shock, but hemorrhage greatly predisposes to 

 shock, and unfortunately it is often impossible to tell from the symptoms alone how 

 much of the latter is present. The diagnosis is clinched by the effect of transfusion; 

 the hemorrhagic case quickly recovers whereas that in shock only slowly, if at all. 



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 con- 

 dition of shock may supervene after a time. In such instances the arterial blood pres- 

 sure remains low and cannot be restored even after an hour or two of artificial respira- 

 tion. 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 anesthetics, such 

 as nitrous oxide gas. A condition closely simulating shock may also be induced in 

 the earlier stages of the administration of anesthetics when these are badly given, but 

 paralysis of the heart or of the respiratory center is a usual cause. 



In cases which have recovered from the shock which often follows immediately after 

 some severe accident, and which is usually called primary shock, the administration 

 of an anesthetic may bring on secondary shock. The danger is least when nitrous oxide 

 is used. 



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 charac- 

 ter, 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 vaso- 

 constrictor 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 

 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 himself 

 by catching flies with his hands. A sufficient description of the condition of spinal 

 shock will be given elsewhere, but here it may be noted that it consists essentially 

 in a paralysis involving at first all of the reflex 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 dog, for 

 example they may all have reappeared. The cause of this shock is no doubt the 

 sudden interruption of the nervous pathways which reflex action ordinarily takes in 

 the higher animals (see page 924). 



5. Toxic Shock. The condition known as anaphylaxis and that which follows the in- 

 jection of histamine into normal animals furnish the best known examples of toxic 

 shock. There is also some strong evidence that a toxic factor is often involved in the 

 causation of clinical shock. The toxic substance may be liberated from a septic 

 process, as in septic peritonitis, or from bruised and mutilated tissue, as after a com- 

 pound fracture. Experience has shown that rapid amputation of a much mutilated 

 limb in a shocked patient has not infrequently ushered in striking changes for the 

 better. The shock which develops in intestinal obstruction has been shown by Whipp 

 and his coworkers to be due to a proteose absorbed from the obstructed loops (see 

 page 538). 



6. Nervous Shock; "Shell Shock." Considerable attention has been paid to the 

 nervous shock that has frequently been observed in men who have been subjected to the 

 harrowing sights and the constant noise and nerve strain incurred in modern warfare. 



