GRAPHIC OF ARTERIAL PRESSURE 



39 



otherwise the preparation will be convulsed or its circulation permanently 

 damaged for the further steps of the exercise. Unclamp or reattach, 

 therefore, the respiratory tube. Almost immediately this is done the colour 

 of the blood in the ai-terial cannula will brighten, the heart-block will cease, 

 and a great rise of a. p. will be shown by the record. This rise is, however, 

 temporary. 



Text-fig. 19. Effect of amyl nitrate on arterial pressure (E. Gloria). 

 A.P., carotid-pressure record by Hg manometer ; z, zero-line of manometer ; 

 T, time in 2" periods ; s, signal-line showing time of injection of amyl nitrite 

 into saphena vein. 



YI. Mix one drop of amyl nitrite with 2 c.c. Ringer-Locke in a watch- Obs. 24. 

 glass. Fill the needle-syringe with the mixture and inject 1 c.c. of it into ^^^ nitrite 

 the saphena vein. The kymograph should be running at the time the pressure, 

 injection is made (text-fig. 19). 



VII. Have ready a glass cannula similar to that used for artery but with Obs. 25. 



rather larger nozzle. Place it on the experiment table in Rinarer-Locke, -"^^^surement 



^ ^ , ^ _ ^ ' of venous 



along with a filler-up pipette. Have ready also three fine cottons in mounted pressure. 



needles. Place the venous manometer on the operation table. 



Expose the external jugular vein low down in the neck, preferably 

 on side opposite to that used for the carotid. 



The fur obscures the contour of the skin, but with the preparation 

 supine and the forelimb retracted feel at the root of the neck just in front of 

 the head of the shoulder. A triangular space can be made out, apex 

 anteriorly. This is the space between the cleidal and sternal portions of 

 sterno-cleidomastoid muscle; they converge as they pass forward. The 



