306 THE CIRCULATION OF THE BLOOD 



creased blood pressure by contracting more slowly and vigorously. Neither 

 is there evidence that the force of the heart beat is in itself diminished. 

 When the organ is exposed it is seen to beat vigorously. Evidently, there- 

 fore, as the cardiac mechanism itself is normal, the deficient discharge of 

 blood must be dependent upon improper diastolic filling. After this con- 

 dition of oligemia has set in, it becomes progressively worse because of 

 weakening of the heart muscle, consequent upon the failing blood supply 

 through the coronary vessels, and this again upon a curtailment of the 

 amount of blood in actual circulation. 



The Cause of the Oligemia. In the first place it is important to recall 

 that mechanical obstruction of the inferior vena cava is followed ulti- 

 mately by the usual signs of shock. Such interference with the venous 

 return to the heart may also possibly be caused by excessive movements 

 of the thorax, as during artificial respiration. That this in itself may lead 

 to shock is known to all experimental investigators on the subject, although 

 the interpretation has not always been that which is given above. Yan- 

 dell Henderson, 32 for example^ thought the excessive ventilation to be 

 the factor responsible for the shock, by causing a blowing off of carbon 

 dioxide from the blood (see page 382) and a consequent low tension of 

 this gas in the blood (acapnia). 



As in gravity shock, so in surgical shock, stagnation of Hood in the 

 splanchnic area is common; the animal bleeds into his own (splanchnic) 

 blood vessels (capillaries and venules), because these have lost their tone. 

 As we have noted above, one of the most certain ways of producing 

 shock is by exposure and rough handling of the abdominal viscera. It 

 is therefore of importance to study the effects that can be noted on 

 the blood vessels of this area under such conditions. When the viscera 

 are first exposed to air, there may be a short period during which vaso- 

 constriction is evident. This is soon followed by a dilatation of the capil- 

 laries and veins as during the first stage of inflammation. The resulting 

 accumulation of blood in the mesenteric veins has been shown by Mor- 

 rison and Hooker to cause an increase in the weight of an isolated loop 

 of intestine as an animal passes into a state of shock. Erlanger and his 

 coworkers insist also on the constant appearance in shocked animals of 

 marked dilatation of the capillaries and venules of the intestinal villi. 

 In the milder forms, the congestion may be confined to the duodenum. 31 



Engorgement of the abdominal vessels alone does not, however, suffice 

 to explain all the curtailment of blood, and we are driven to the con- 

 clusion that much is lost in the capillaries of the tissues outside the abdo- 

 men. As a matter of fact, Cannon and others have found that concentra- 

 tion of the blood occurs in these capillaries, as indicated by comparisons 

 of the percentage of corpuscles and hemoglobin in blood drawn from veins 



