Cfc. XX.] 



UOY'S TONOMETER. 



259 



the top of which is a writing style. The apparatus is arranged so that the 

 movements of the mercury can be recorded by the float and the writing style 

 on a slowly revolving drum. The movements 

 of the mercury are due to change in the 

 endocardiac pressure. 



The other two instruments we shall describe 

 are constructed on the opposite principle : the 

 heart is enclosed in a chamber filled with oil, 

 and the movements of this oil outside the 

 heart are registered. 



(2) Roy't Tonometer (fig. 256) : 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 junc- 

 tion 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 



Fig. 255. Kronecker's Perfusion 

 Cannnla, 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 

 ia tied to the outer tube of the 

 cannula, a current of liquid can 

 be made to pass into the heart 

 by one tube and out through the 

 other. 



Fig. 256. Roy's Tonometer. 



which passes a wire, which is attached to a lever (cut short in the .diagram) 

 fi xcd on a stage below the apparatus. 



s 2 



