CH. XX.] 



ROY'S TONOMETER 



257 



the fluid enters by one and leaves by the other tube. Numerous 

 instruments have been devised for obtaining graphic records of the 

 heart's movements under these circumstances, but we shall be content 

 with describing a few of the best. They have been much used in the 

 investigation of the effects of drugs on the heart, and the results 

 obtained have been of much service to physicians. 



(1) The heart having been securely tied on to the perfusion cannula, the 

 circulating fluid is passed through <it. One stem of the cannula is then attached 

 by the small side branch on the left in fig. 263 by a tube containing salt solution to 

 a small mercurial manometer, provided with a float, on the top of which is a writing 

 style. The apparatus is arranged so that the movements of the mercury can be 



FIG. 263. Krouecker's Perfusion 

 Cannula, for supplying fluids 

 to the interior of the frog's 

 heart. 



It consists of a double tube, 

 one outside the other. The inner 

 tube branches out to the right; 

 thus, when the ventricle is tied 

 to the outer tube of the cammla, 

 a current of liquid can be made 

 to pass into the heart by one tube 

 and out through 



,eart by one 

 the other. 



Fio. 264. Boy's Tonometer. 



recorded by the float and the writing style on a slowly revolving drum. The move- 

 ments of the mercury are due to changes in the intracardiac pressure. 



(2) Roy's Tonometer (fig. 264) : A small bell-jar, open above, but provided with 

 a firmly fitting stopper, in which is fixed a double cannula, is adjustable by a 

 smoothly ground base upon a circular brass plate, about 2 to 3 inches in diameter. 

 The junction is made complete by greasing 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 

 with a stop-cock. The opening provided with the collar is closed at the lower part 

 with a membrane, which is closely tied by means of a ligature around the groove 

 at the lower edge of the collar. To this membrane a piece of cork is fastened by 

 sealing-wax, from which passes a wire, which is attached to a lever (cut short in 

 the diagram) fixed on a stage below the apparatus. 



When using the apparatus, the bell-jar is filled with olive-oil. The heart of a 

 large frog is prepared and the cannula fixed in the stopper is firmly tied into it ; 

 the tubes of the cannula communicate with the reservoir of circulating fluid on the 

 one hand, and with a vessel to receive it after it has run through the heart on the 



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