CHAP, 



RESPIRATION. 



505 



with the cardiometer, being increased. The slowing of the 

 rhythm is in part due to vagus inhibitory action, the too 

 venous blood exciting the bulbar cardio-inhibitory centre ; for 

 the effect is much less when both vagus nerves are divided. 

 But as illustrated by Fig. 100, which is a curve of blood-pressure 



FIG. 100. 



BLOOD-PRESSURE CURVES DURING A SUSPENSION OF BREATHING. 

 TRAUBE-HERING CURVES. 



The curves 1, 2, 3, 4, 5 are portions selected from one long continuous tracing 

 forming the record of a prolonged observation, so that the several curves repre- 

 sent successive stages of the same experiment. Each curve is placed in its 

 proper position relative to the base line, which, to save space, is omitted ; and 

 it is obvious that, starting from the stage represented by 1, the blood-pressure 

 rises in stages 2, 3, and 4, but falls again in stage 5. Curve 1 is taken from 

 a period when artificial respiration was being kept up, and the undulations 

 visible are those the nature of which has been discussed; the vagus nerves 

 having been cut the pulsations on the ascent and descent of the undulations do 

 not differ. When the artificial respiration was suspended these undulations dis- 

 appeared, and the blood-pressure rose steadily while the heart-beats became 

 slower. Soon, as shewn in curve 2, new undulations appeared. A little later, 

 the blood-pressure was still rising, the heart-beats still slower, but the undula- 

 tions still more obvious (curve 3). Still later (curve 4), the pressure was still 

 higher, but the heart-beats were quicker, and the undulations flatter. The pres- 

 sure then began to fall rapidly (curve 5), and continued to fall until some time 

 later artificial respiration was resumed. 



during asphyxia after division of both vagus nerves, the effect 

 is not wholly done away ; the slowing is in part due to other 

 causes, but what these are is not very clear. 



These changes in the heart in no way explain the rise of 



