274 THE CIRCULATION OF THE BLOOD 



Lombard determines the end point in this experiment more accurately 

 by the aid of a low power binocular microscope after rubbing vaseline into 

 the skin to increase its transparency. Hooker's method of compressing 

 the capillaries by an air system controlled and measured by a manometer 

 allows measurement both during compression and in decompression. This 

 method has been adapted to the mammalian mesentery by Ellis. 



21. The Arterial Blood -Pressure in a Mammal and Its Nervous 

 Regulation. After the student has measured the arterial blood-pres- 

 sure by Hale's method, described above, he is in a position to study the 

 variations and co-ordinations in the blood circulatory apparatus. The re- 

 cording apparatus consists of writing pens, seconds time marker, signal 

 marker, blood-pressure manometer preferably Ludwig's mercury manom- 

 eter, and a continuous paper kymograph preferably Ludwig's weight- 

 driven form or the Harvard belt kymograph for a continuous record of the 

 arterial blood-pressure. Connect the cannula with the mercury man- 

 ometer which is provided with a pressure bottle. Use a cannula of the 

 form shown in figure 185, connecting the side limb of the cannula with the 

 mercury manometer, and the end limb with the pressure bottle. When 

 the apparatus is ready chloretonize and anesthetize a mammal (dog, cat, or 

 rabbit), and bind it to the animal-holder. Let one operator attend strictly 

 and at all times to the anesthetic, for the animal must not under any condition 

 recover consciousness during the experiment. 



Expose the carotid artery in the neck, as described in Experiment 13 

 above, arrange it with ligatures for inserting the cannula, expose the 

 vagus nerve with the same care, and throw ligatures around it for con- 

 venience in lifting it out of its bed. Make a V-shaped cut in the carotid 

 directed toward the heart, insert and ligate the cannula as previously 

 described. Before beginning the experiment one should see that all the 

 tubes are filled with the anticoagulating liquid and that the manometer is 

 under pressure from 130 to 140 mm. mercury. When all is ready start the 

 kymograph, see that the recording pens are properly adjusted, remove the 

 bulldog forceps from the artery, and the pressure record will begin. 



a. Take a tracing of the normal arterial pressure and heart rhythm with 

 the recording paper moving at the rate of 0.5 cm. per second. 



b. Stimulate the right vagus nerve with a mild induction current for 

 10 seconds. If this stimulus is strong enough to produce change in blood- 

 pressure or inhibitions of the heart-rate, then allow sufficient time follow- 

 ing the stimulus for the blood-pressure to return to the previous normal. 

 Observing these rules, vary the intensity of the stimulus from that which 

 produces no apparent effect to that which produces complete inhibition of 

 the heart. Vary the time of the stimulus through i, 5, io,and 20 seconds, 

 using different strengths. Do not allow the nerve to cool, become dry, 

 or to be unduly stretched. 



