290 RESPIRATION 



harmful disintegration products,^* and Dale and Laidlaw have 

 shown that similar symptoms are caused by the action of histamine 

 produced by tissue disintegration.^^ In "histamine shock" the 

 venous return to the heart is inadequate, just as in acapnial shock, 

 and blood appears to stagnate in dilated capillaries so that the 

 rest of the vascular system is imperfectly filled with blood. Dale 

 and Laidlaw regard the dilatation of capillaries as a primary ac- 

 tion of the poison. The respiratory center seems, also, to be affected 

 very quickly, so that artificial respiration is needed to keep the 

 animal alive. How far the failure of the respiratory center is 

 consequent on failure of the circulation, or vice versa, it seems 

 difficult at present to say ; but the shallow breathing and leaden 

 cyanosis in shock are indicative of advancing failure of the re- 

 spiratory center, and appear to be clear indications for early 

 and continuous oxygen administration, if the condition cannot be 

 dealt with by removing its cause or in other ways. To remedy the 

 imperfect filling of the vessels and consequent failure of the circu- 

 lation, there is an equally clear indication for the intravenous 

 injection of gum-saline solution. Whether the administration of 

 air containing CO2 would be of service, as in shock due to simple 

 alkalosis, is not yet known. If the respiratory center is injured by 

 a poison from the injured tissues it may be unable to respond 

 properly to the CO2. 



Dale found that the danger from histamine shock may be enor- 

 mously increased by the administration of an anaesthetic. Many of 

 Henderson's observations seem to point in the same direction as 

 regards acapnic shock. These investigations throw much light on 

 the fatal accidents of anaesthesia. 



In connection with circulation and breathing it is important to 

 consider the manner in which the volume and haemoglobin per- 

 centage of the blood adjust themselves under varying conditions. 

 They are fairly constant within about five per cent under ordinary 

 conditions for any individual, and the volume of blood in a mam- 

 mal bears a pretty constant ratio to the body weight. This propor- 

 tion does not depend upon size or ratio of body weight to surface, 

 since it is about the same in large as in small mammals. Thus 

 in the rat or mouse the proportion is about the same as in man. 



In a small warm-blooded animal such as a mouse the metabolism 

 per gram of body weight is enormously greater than in a large 



^Report No. VIII of Surgical Shock Committee (Special Report No. 26 of 

 Medical Research Committee) , 1919. 



"Dale and Laidlaw, Journ. of Physiol., LII, p. 355, 19 19. 



