226 



EXPERIMENTAL PHYSIOLOGY. 



(b.) If the "heart-apex" preparation does not contract 

 spontaneously, stimulate it by e.g., single induction 

 shocks either make or break. To this end adjust an 

 induction machine, the wires from the secondary coil being 

 attached, one to the cannula itself, while the other is placed 

 in the fluid in the glass cup, into which the heart is lowered. 



(c.) By introducing an electro-magnet Avith a recording 

 lever into the primary circuit (Lesson XXXI.), and having 

 a time-marker recording at the same time, one can determine 

 the latent period of the apex preparation. It is about 

 0-15 sec. 



(d.) If desired, the effect of a constant current may be 

 studied in this way instead of by the method described in 

 Lesson XLVIII., 2. The apex beats rhythmically under the 

 influence of the constant current. 



LESSON LI. 

 TONOMETER GASKELL'S CLAMP. 



1. Roy's Frog-Heart Apparatus or Tonometer. This apparatus 

 registers the change of volume of the contracting heart. Fig. 

 105 shows a scheme of the apparatus. The apparatus consists 

 of a small bell-jar, resting on a circular 

 brass plate about 2 inches in diameter, 

 and fixed to a stand adjustable on an 

 upright. In the brass plate are two 

 openings, the small one leads into an out- 

 let tube (e), provided with a stop-cock. 

 The other is in the centre of the plate, 

 and leads into a short cylinder 1 cm. in 

 length by 1 cm. in internal diameter. 

 A groove runs round the outside of this 

 cylinder near its lower edge, to permit of 

 a membrane being tied on to it. In this 

 cylinder works a light aluminum piston 

 (p), slightly less in diameter than the 

 cylinder. Around the lower aperture 

 of the cylinder 

 is tied a piece 

 of flexible 

 animal mem- 



Fig. 105. Roy's Tonometer. 



