APEX PREPARATION. 



225 



(b.) Arrange a frog's mercury manometer provided with 

 a writing-style as in Fig. 104. Attach the inlet tube of the 

 cannula to the Marriotte's 

 flasks (a, b), and connect 

 the outflow with the tube 

 of the mercury manometer. 

 It is well to have a T-tube 

 between the heart and the 

 manometer, but in the 

 heart apparatus, as shown 

 and used, the exit tube is 

 preferable. See that 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 movements 

 on a slow-moving drum. 



(c.) Take a tracing with 

 the outflow tube and Fig. 104. 



Marriotte's flask shut off, 



so that the whole effect of the contraction of the heart is 

 exerted upon the mercury in the manometer. Take another 

 tracing when the fluid is allowed to 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 stop-cock (s) one can pass either the one 

 fluid or the other through the heart. The little cup (<:/) 

 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 preparation of the heart only the 

 apex of the heart is used. As a rule, it does not beat spontane- 

 ously until sufficient pressure is applied to its inner surface by 

 the fluid circulating through the heart. 



(a.) Proceed as in Lesson XLIX., 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-ventricular groove. Excise 

 the heart and cannula, and attach it to the heart apparatus 

 as in the previous experiment. 



15 



