THE CIRCULATION. 309 



heart-action. If the pneumogastrics are divided the pulse-frequency 

 increases, and as a result the arterial tension rises. If the vagi are 

 irritated the pulse-rate falls and as a sequence the arterial tension 

 diminishes. 



Eyster and Hooker found that the slowing of the heart in 

 animals with intact vagi from increase of arterial pressure is due to 

 two facts which normally act together: (1) a direct effect of the 

 increased blood-pressure upon the cardio-inhibitory center; (2) a 

 stimulation of the cardio-inhibitory center through the afferent 

 nerves, resulting in a reflex slowing of the heart. The afferent 

 path of the reflex has its origin, at least to a great extent, in the 

 thoracic aorta. The reflex slowing of the heart from increase of 

 arterial pressure persists after section of the accelerator and depres- 

 sors. The afferent path of this reflex is in part of fibers contained in 

 the vagus. 



Lecrenier has confirmed these observations. 



The reciprocal power of the pulse and blood-pressure to regulate 

 each other depends on normal pneumogastrics. 



Pathological. In cases of granular or contracted kidney, sclerosis 

 of the arteries, and where digitalis is used in heart affections, the 

 blood-pressure is raised. Injected ergotin, by causing contraction of 

 the arterioles, also raises pressure, while morphine lowers the same. 

 The blood-pressure falls in the ending of fevers. 



Capillary Blood-pressure. Yon Kries has estimated the blood- 

 pressure in the capillaries of the ear to be about 22 millimeters of 

 mercury. 



The pressure is greatest in the lower extremities, hence we have 

 an increased transudation from them or even rupture. 



Water or blood extravasated in the sub-con junctival tissues are 

 often the result of the high blood-pressure in chronic Bright's disease. 

 Capillary pressure is regulated more by the blood-pressure in the veins 

 than in the arteries. Gravity increases pressure in the capillaries. 



Pathological Action. In a feeble heart with retrograde pressure 

 in the veins increased, the slow capillary flow of blood receives an 

 excess of carbonic acid and cyanosis of the skin ensues. 



Venous Blood-pressure. Since the pressure is so low (even nega- 

 tive in places) within this system, a saline solution is usually sub- 

 stituted in the manometer for mercury. The kymographic tracing 

 taken near the heart shows the characteristic large and small waves, 

 with this difference, however, that the respiratory rise accompanies 

 expiration. 



