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A MANUAL OF PHYSIOLOGY 



drum, so that it hangs down outside of the writing-point of the 



manometer-float and always keeps it in contact with the smoked 



surface without undue friction. Or a 



piece of glass rod drawn out to a fine 



thread in the blowpipe flame answers 



very well. Below the writing-point of 



the float, and in the same vertical line 



with it, adjust the writing-point of a 



time-marker beating seconds (Fig. 76, 



P- i?9). 



Next, fasten the animal on a holder, 

 back down. Give ether and insert a 

 tracheal cannula (p. 186) . (The tracheal 

 cannula is not absolutely required for 

 the experiment, but it is convenient, as 

 the animal is more under control, and 

 artificial respiration can be begun at any 

 moment, should this be necessary.) 

 Insert a glass cannula, armed with a 

 short piece of rubber tubing, into the 



A 



FIG. 92. THREE-WAY CANNULA. 



central (cardiac) end of the carotid 

 artery (p. 55). Leaving the bulldog 

 forceps on the artery, fill the cannula 

 and tube with the sodium citrate or 

 one of the other solutions. Slip the 

 rubber tube over a short glass connect- 

 ing-tube. Fill this also with the solu- 

 tion, and connect it with the mano- 

 meter-tube, seeing that both are quite FIG. 93. MANOMETER WITH 

 full of liquid, so that no air may be SIDE-TUBE (GUTHRIE). 



enclosed. A > fl o at B > collar through 



Where a permanent working place is which the wire C of the float 

 provided for blood-pressure experiments moves; D, vertical wire fixed 

 it is convenient to connect the cannula 

 and manometer with a pressure-bottle 

 containing the sodium citrate solution, 

 and to use a three-way cannula for 

 the bloodvessel (Fig. 92). The cannula 

 has a bulbous enlargement, which hinders clotting. The end of the 

 cannula is connected with the tube from the pressure-bottle, which 



to manometer - holder, which 

 keeps the writing-point on the 

 drum ; E, limb of manometer 

 connected with cannula, with 

 its side-piece, F. 



