184 THE BODY AT WOEK 



filled with water. It is a wise precept that artificial respiration 

 should be tried in every case, without waiting a single instant 

 to ascertain whether the heart still beats. The first thing to 

 do is to empty the chest of water. Then place the subject on 

 his back. Kneel on the ground behind his head. Grasp an 

 arm just below the elbow, in each hand. Draw the arms up 

 above the patient's head, so that the pectoral and other muscles 

 drag on the ribs, enlarging the chest ; then lower them, and 

 press them into the sides. This must be done with the natural 

 rhythm of respiration, and not more frequently than twenty 

 times in a minute. It is well if an assistant draws the tongue 

 forward, to give free admission to air. Presumably the 

 slight exchange of air brought about by mechanical expansion 

 and compression of the chest favours the passage of blood 

 through the capillaries of the lungs ; but the real object of 

 artificial respiration is to stretch the endings of the vagus nerve, 

 and in this way to originate impulses which will call the 

 respiratory centre into action. Perhaps it may not be super- 

 fluous to point out that the failure of the pulse must not be 

 taken as an indication that the heart has ceased to beat. 

 Owing to the obstruction to the circulation through the lungs, 

 the left side of the heart is almost empty. Very little blood is 

 pumped into the aorta. None reaches the wrist. 



Exchange of Gases in the Lungs. In the lungs each red 

 corpuscle takes from the air a charge of oxygen which it carries 

 to the tissues. In the tissues the plasma of the blood receives 

 carbonic acid, which escapes from it when it reaches the lungs. 

 Water dissolves oxygen and carbonic acid. Towards animals 

 and plants which live in it, water plays the same role as the 

 atmosphere towards dwellers on land. The quantity of a gas 

 which will dissolve in water is proportional to the pressure to 

 which it is subjected. If water were the circulating fluid, some 

 oxygen would enter it in the lungs ; some carbonic acid would 

 be taken up in the tissues and liberated in the lungs. But it 

 is clear that the small quantity of fluid which the vascular 

 system will hold would be incapable of serving as an efficient 

 medium of exchange between the tissues and the lungs. 

 When a given quantity of venous blood is agitated with air, 

 five times as much oxygen is taken up as the blood could 

 carry if the gas were simply dissolved. Both oxygen and 



