264 PRACTICAL PHYSIOLOGY. [LIIL 



2. Auricular Contraction. — Take a tracing with the lever 

 adjusted on the auricles alone, and avoid the bulbus aortae. Note 

 the smaller excursion of the lever. 



3. Ventricular Contraction. — Adjust the lever so as to obtain 

 a tracing of the ventricular movements only. 



4. lu the above experiments arrange an electro-magnetic time- 

 marker or chronograph under the recording lever, so that the poiuts 

 of tlie recording lever and time-marker write exactly in the same 

 vertical line. Thus one can calculate the time-relations of any part 

 of the curve. 



5. Effect of Temperature on the Excised Heart. 



- (a.) Excise the heart of a pithed frog, lay it on an apparatus like 

 that in fig. 119. Fix india-rubber tubes to the inlet and outlet 

 tubes of the cooling-box, the inlet tube passing from a funnel fixed 



FlQ. 1S4.— Parts of a Tracing taken from an Excised Frog's Heart. The temperature 

 was increased gradually from left to right of the curve. 



in a stand above the box, and the outlet tube discharging into a 

 vessel below it. Adjust the heart-lever to record the movements 

 of the contracting ventricle on a slowly-revolving drum. If the 

 heart tends to become dry, moisten it with normal saline mixed 

 with blood. Adjust a time-marker. Take a tracing. 



(b.) Pass water from io°-2o° C. through the cooling-box, noting 

 the effect on the number of contractions, and the duration, height, 

 and form of each single beat. 



(0.) The heart may be placed on a metallic support and gradually heated 

 by means of a spirit-lamp or other means. Fig. 184 shows how the shape, 

 size, amplitude, and number of heart-beats varies with a rise of temperature, 

 the temperature being lowest towards the left end of the tracing, and rising 

 as the tracing was taken. 



