LIX.] 



ENDOCARDIAL PRESSURE. 



283 



on to it. In this cylinder works a light alnnunium piston (p), slightly less in 

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

 a piece of flexible animal membrane, the liga- 

 ture resting in the grooved collar. The free 

 I)art of the membrane is tied to the piston, from 

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



f)asses down to be attached to a light writing- 

 ever (/) fixed below the stage. The bell-jar is 

 filled with oil {o), while in its uj)per opening is 

 fitted a short glass stoj)iier, })ertbrated to allow 

 the passage of a two-wayed heart-cannula with 

 the heart attached (A). 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 ; 



y afterwards the lower 



.L . end of the membrane 



is fixed to the pis- 

 ton, taking care that 



FlQ. 205. — Scheme of K.oy's Tonometer. 



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

 in a little glycerin to moisten the membrane. 



FlO. 206.— Hoy's Tonometer, as made by the Cambridge Scientific 

 Instrument Company. 



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

 adjusted. Prepare the heart of a large frog [Lesson LVIIL (a.), {b.) (omit c), 



