282 



PRACTICAL PHYSIOLOGY. 



[lix. 



no air-bubbles are present in the system. Every time the heart contracts 

 the mercury is displaced and the writing style is raised, and records its move- 

 ments on a slow- moving drum. 



(r.) Take a tracing with the outflow tube and Marriotte's flask shut ofi", so 

 that the whole efi"ect of the contraction of the heart is exerted upon the 

 mercury in the manometer. Take another tracing when the fluid is allowed 

 i.0 flow continuously through the heart. The second Marriotte's flask shown 

 in the figure is for the perfusion of fluid of a different nature, and by means 

 of the stojKJOck (s) one can pass either the one fluid or the other through the 

 heart. The little cup {d) under the heart can be raised or lowered, and filled 

 with the nutrient fluid, and in it the heart is bathed. 



2. Apex Preparation. — In this pre- 

 paration of the heart only the apex 

 of the heart is used. As a rule, it 

 does not beat spontaneously until 

 suflBcient pressure is api)lied to its 

 inner surface by the fluid circulating 

 through the heart. 



(a.) Proceed as in Lesson LVIII. 2 

 (a.), (b.) (omit c), {d.), with this 

 difference, that in {d.) the cannula 

 is placed deeper into the ventricle, 

 and the ligature is tied round the 

 ventricle below the auriculo-ventricu- 

 lar groove. Excise the heart and 

 cannula, and attach it to the heart 

 apparatus as in the previous experi- 

 ment. 



(6.) If the "heart a])ex" prepara- 

 tion 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 with a recording lever into the 



primary circuit, and having a time-marker recording at the same time, one 



can detennine the latent period of the apex preparation. It is about 0.15 



sec. 

 (d.) If desired, the eff'ect of a constant current may be studied in this way 



instead of by the method described in Lesson LVI. 2. The apex beats 



rhythmically under the influence of the constant current. 



Fia. 204.— Scheme of Kronecker'8 Frog 

 nanometer. 



3. Roy's Frog-Heart Apparatus or Tonometer. — This apparatus registers 

 the change of volume of the contracting heart. Fig. 205 shows a scheme of 

 the apparatus, and fig. 206 the apparatus itseli. 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 biass plate are two 

 openings, the small one leads into an outlet 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 i cm. in internal diameter. A groove runs round the out- 

 side of this cylinder near its lower edge, to permit of a membrane being tied 



