DETERMINATION OF THE RESPIRATORY EXCHANGE 323 



sociation of oxyhsemoglobin. In. particular, by locally increasing the 

 acid in the blood within the capillaries, the hard-working tissues 

 dissociate oxygen from the oxyhsemoglobin and make the red corpuscle 

 discharge its cargo of oxygen with rapidity. At the same time, by 

 increasing the general acidity of the blood, the tissues provoke the 

 respiratory centre to increased activity. The increased acidity of the 

 blood not only modifies the dissociation curve of oxyhsemoglobin, but 

 is accompanied by a lower percentage of C0. 2 in the alveolar air, a 

 lower respiratory quotient, and diminished power of the haemoglobin 

 to combine with oxygen in the lungs. 



Artificial Respiration. In this country two methods are in vogue. 

 In the older method Sylvester's the subject is placed on his back, 

 with a pillow or folded garment beneath the shoulders. The tongue 

 is pulled well forward, the mouth kept open. Inspiration is induced 

 by grasping the arms below the elbow, and gradually raising them 

 above the head (Fig. 181 ). Expiration is produced by bending the arms, 



FIG. 183. CAT: RECORD OF RESPIRATION. 



A, Chloroform on between the arrows; B, C0. 2 on between the arrows; C, C0 2 on again. 



Time in seconds. 



and pressing them forcibly against the chest wall (Fig. 18lA). These 

 operations should be performed about twenty times a minute. The 

 method has the disadvantage of being fatiguing to the operator. 



The more recent method Schafer's has largely overcome 

 this defect. In it the subject is placed face downwards, with the 

 upper part of the chest raised by a pillow or some similar support. 

 The operator stands at the side of the subject facing his head ; then> 

 placing his hands on the lowest ribs on either side, he slowly brings 

 the weight of his body to bear upon his own arms, and thus presses 

 upon the thorax of the subject, and forces air out of the lungs. Then 

 he gradually relaxes the pressure by bringing his own body up again 

 to a more erect position without moving the hands (Fig. 182). 



The rhythmic pressure on the thorax helps to squeeze blood through 

 the heart and lungs, and it is as important to effect this as it is to intro- 

 duce air. The excitatory effect of CO^ upon the respiration might 

 be made use of in cases of poisoning due to oxygen-want (carbonic 



