ADVANCED EXPERIMENTAL PHYSIOLOGY 353 



tension, when the ventricle is raising the blood pressure up to that in 

 the aorta. The beginning of the dicrotic notch corresponds with the 

 closure of the aortic valves and the end of output. The time lost in the 

 transmission of the pulse-wave from the heart to the carotid artery 

 should be deducted in making these time measurements, but it is almost 

 negligible. In a man with a pulse frequency of 70 the duration of 

 systole was 0-379 sec., of diastole 0-483 sec. It is interesting to repeat 

 the observations after the frequency of the heart has been accelerated 

 by running up and down stairs. The diastolic period is shortened 

 much more than the systolic period. When the pulse frequency varied 

 in the proportion 100 : 270 the duration of a systole varied in the pro- 

 portion 136 : 100. 



CHAPTER XXVII. 

 BLOOD PRESSURE. 



Blood Pressure in Frog. Pith the cerebrum of a large frog and plug 

 the hole, and then curarise lightly. Fill the fine glass cannula provided 

 with sodium citrate, 1 per cent, sol., and clip the rubber tube. Pass 

 two ligatures under one of the aortae. Tie the peripheral one as far 

 from the bulbus arteriosus as possible. Pull up the other ligature 

 (placed near the bulbus) so as to constrict the vessel. Between the 

 two ligatures make a V-shaped slit into the artery with sharp scissors. 

 Insert the cannula and tie the ligature round it. Do not allow any 

 loss of blood. 



Fill the proximal limb and rubber tube of the mercurial manometer 

 with 1 per cent. sol. sodium citrate. Place the frog board so that 

 the arterial cannula is on a level with the mercury meniscus, and con- 

 nect the tube of the latter with the tube of the manometer. Remove 

 the clip. The mercury rises until it balances the blood pressure, and 

 oscillates with each ventricular systole. 



Bring the writing point of the manometer against a slowly moving 

 drum. 



Observe the effect of gently compressing the abdomen. This in- 

 creases both the diastolic filling of the heart and the resistance to 

 systolic outflow. Reflexly inhibit the heart by lightly and frequently 

 striking the abdomen with the handle of a scalpel. The heart distends 

 with blood and arterial pressure falls owing to lessened systolic output. 



Inhibition may also be brought about by tetanising the sino-auricular 



