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HANDBOOK OF PHYSIOLOGY. 



similar tube, which communicates by a T piece with a small mercurial man- 

 ometer, provided with a writing style, and also with a vessel into which the 

 serum 'is received. The apparatus being arranged so that the movements of 

 the mercury can be recorded by the float and the writing style on a slowly 

 revolving drum, and after some serum has been allowed to pass freely through 

 the ventricle, both tubes are clipped, the second one beyond the T piece, and 

 the alterations in the pressure are recorded. The effects of fluids at various 

 temperatures and of poisons may be recorded in the manner indicated above. 



(3) By Roy's Tonometer (fig. 197) the alterations in volume which a frog's 

 heart undergoes during contrac- 

 tion are recorded by the follow- 

 ing means: A small bell-jar, 

 open above, but provided with a 

 firmly fitting cork, in which is 

 fixed a double canula, is ad- 

 justable by a smoothly ground 

 base upon a circular brass plate, 



Fig. 196. 



Fig. 197. 



Fig. 196. Kronecker's Perfusion Canula. for supplying Fluids to the interior of the Frog's 

 Heart. It consists of a double tube, one outside the other; the end view is shown in the engraving. 

 The inner tube branches out to the left: thus, when the ventricle is tied to the outer tube of the can- 

 ula, a current of liquid can be made to pass into the heart by one tube and out through the other. 



Fig. 197. Roy's Tonometer. 



about 2 to 3 inches in diameter. The junction is made complete by greas- 

 ing the base with lard. In the plate, which is fixed to a stand adjustable on 

 an upright, are two holes, one in the centre, a large one about one-third 

 of an inch in diameter, to which is fixed below a brass grooved collar, 

 about half an inch deep ; the other hole is the opening into a pipe provided 

 w ith a tap (stopcock) . The opening provided with the collar is closed at the 

 lower part with a membrane of animal tissue, which is loosely tied by means 

 of a ligature around the groove at the lower edge of the collar. To this mem- 

 brane a piece of cork is fastened by sealing-wax, from which passes a wire, 

 which can be attached to a lever, fixed on a stage below the apparatus. 



When using the apparatus, the bell-jar is fixed by means of lard, and the 

 jar is filled with olive oil. In the way above described, the heart of a large 

 frog is prepared and the canula fixed in the cork is firmly tied into the heart ; 

 the tubes of the canula communicating with the reservoir of serum on the 

 o^ie hand, and with a vessel to contain the serum after it has run through on 

 tho other. The canula with heart attached is passed into the oil, and the 

 cork firmly secured. By these means the lever will be found to be adjusted to 



