264 PRACTICAL PHYSIOLOGY. fLIII. 



2. Auricular Contraction. Take a tracing with the lever 

 adjusted on the auricles alone, and avoid the bulbus aortse. 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. In the above experiments arrange an electro-magnetic time- 

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

 of the 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. 184. 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. 



(6.) 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. 



(c.) 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. 



