GASKELL'S CLAMP. 227 



brane, the ligature resting in the grooved collar. The free part 

 of the membrane is tied to the piston, from the centre of whose 

 under-surface (p) a needle passes down to be attached to a light 

 writing-lever (/) fixed below the stage. The bell-jar is filled with 

 oil (0), while in its upper opening is fitted a short glass stopper, 

 perforated to allow the passage of a two-wayed 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 trans- 

 parent membrane such as is used by perfumers for cover- 

 ing 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 piston, taking care 

 that the needle attached to the piston hangs towards the 

 recording lever. Drop in a little glycerin to moisten the 

 membrane. 



(6.) Fill the jar with olive oil, and have the recording ap- 

 paratus ready, adjusted. Prepare the heart of a large frog 

 [Lesson XLIX., (a.), (b.), (omit c.), (c?.)], the caimula used 

 being one fixed in the glass stopper of the bell-jar, and 

 attach the inlet tube of the cannula to the reservoir of 

 nutrient fluid, while the outlet tube is arranged so as to allow 

 fluid which has passed through the heart to drop into a 

 suitable vessel. 



(c.) Introduce the camiula, with the heart attached, into 

 the oil, and see that the stopper is securely fixed. Open the 

 stop-cock (e), and allow some oil to flow out of O, thus render- 

 ing the pressure within sub-atmospheric; and as soon as 

 the pressure has fallen sufficiently, and the little piston is 

 gradually drawn up to the proper height, close the stop-cock. 

 Attach the needle of the piston to the recording light lever, 

 and take a tracing. 



2. GaskelTs Clamp. 



(a.) On a suitable support arrange two ordinary recording 

 long, light levers of the same length, and with their writing- 

 points exactly in the same vertical line, recording on a slow- 

 moving drum, the levers being about 12 cm. apart. About 



