LIX.] 



ENDOCARDIAL PRESSURE. 



283 



on to it. In this cylinder works a light aluminium piston (p\ slightly less in 

 diameter than the cylinder. Around the lower aperture of the cylinder is tied 

 a piece of flexible animal membrane, the liga- 

 ture resting in the grooved collar. The free 

 part of the membrane is tied to the piston, from 

 the centre of whose under-surface (/>) a needle 

 passes down to be attached to a light writing- 

 lever (I) fixed below the stage. The bell-jar is 

 filled with oil (o), while in its upper opening is 

 fitted a short glass stopper, perforated to allow 

 the passage of a two-waved heart-cannula with 

 the heart attached (h}. In using the instrument 

 proceed as follows : 



(a.) Fix the bell-jar to the circular brass 

 plate by the aid of a little stiff grease. Tie a 

 piece of the delicate transparent membrane 

 such as is used by perfumers for covering the 

 corks of bottles in the form of a tube round 

 the lower end of the 

 grooved cylinder ; 

 afterwards the lower 

 end of the membrane 

 is fixed to the pis- 

 ton, taking care that 

 the needle attached to the piston hangs towards the recording lever. Drop 

 in a little glycerin to moisten the membrane. 



FIG. 205. Scheme of Roy's Tonometer. 



FIG. 206. Roy's Tonometer, as made by the Cambridge Scientific 

 Instrument Company. 







(ft.) Fill the jar with olive-oil, and have the recording apparatus ready 

 adjusted. Prepare the heart of a large frog [Lesson LVIII. (a.), (6.) (omit c.), 



