508 DEFICIENT ARTEKIALIZATION. [BOOK n. 



whose breathing is fairly normal. We need not discuss them 

 any further now, and have introduced them chiefly to illustrate 

 the fact that the vaso-motor nervous system is apt to fall into a 

 condition of rhythmic activity. 



FIG. 101. BLOOD-PRESSURE CURVE OF A RABBIT, RECORDED ON A SLOWLY 

 MOVING SURFACE, TO SHEW TRAUBE-HERING CURVES. 



(The curve was described not by means of a mercury manometer, but by an 

 instrument similar to but not identical with Fick's spring-kymograph.) In each 

 heart-beat the upward and downward stroke are very close together but may be 

 easily distinguished by the help of a lens. The undulations of the next order 

 are those of respiration. The wider sweeps are the Traube-Hering curves, of 

 which two complete curves and portions of two others are shewn. Each Traube- 

 Hering curve comprises about nine respiratory curves, and each respiratory curve 

 about the same number of heart-beats. 



316. While changes occurring primarily in the respira- 

 tory system thus affect the vascular system, conversely changes 

 occurring primarily in the vascular system affect the respira- 

 tory system. 



Of these the most common and important however are 

 changes in the circulation through the lungs. In the normal 

 organism an adequate supply of arterial blood to the tissues 

 is secured by an adequate renewal of the air in the pulmonary 

 alveoli and an adequately rapid flow of blood through the pul- 

 monary capillaries. When, as by obstruction in the pulmonary 

 arteries, or by failure of the cardiac valves, or, and perhaps 

 especially, by an insufficient cardiac stroke, the stream of blood 

 from the lungs into the left ventricle is lessened either in 

 amount or in rapidity, less oxygen is carried to the tissues, 

 including the nervous tissue of the spinal bulb, and dyspnoea or 

 " want of breath " follows. When the circulation through the 

 lungs is in full healthy swing, the haemoglobin of the red cor- 

 puscles is as we have seen saturated or nearly saturated with 

 oxygen. If owing to a slower stream the red corpuscles tarry 

 longer in their passage along the walls of the pulmonary alveoli 

 they cannot thereby take up a compensating addition of oxy- 

 gen, indeed it is doubtful if they can take up any additional 

 oxygen at all. The blood falling under these circumstances 



