CIRCULATION OF THE BLOOD. 



ably include also a tracing of the auricular contraction and, if the 

 counterpoise is delicate enough, the sinus may likewise be included. 



Note the relation and sequence of contraction of sinus, auricles, 

 and ventricle. 



With direct transmission, the relations of auricular pulsation to 

 ventricular systole and diastole may be observed by placing the 

 foot of the writing lever upon the auriculo-ventricular groove. 



The relation of ventricle to bulbus contraction may be shown in 

 the same way, by adjusting the foot of the lever to rest partly upon 

 the ventricle and partly upon the bulbus. 



Make careful record of all observations and interpretations of re- 

 sults, marking all data necessary for identification upon the tracing. 



Compare your results with those of other students and explain 

 differences. 



What part of the tracing is due to errors of adjustment of, and 

 inertia of, the apparatus ? 



IV. INFLUENCE OF TEMPERATURE UPON THE BEAT OF THE 

 FROG'S HEART. 



Use the same heart as in the previous experiment, or, if this is not 

 vigorous enough, make a fresh preparation. 



Record the beat of the ventricle, taking a time tracing in seconds 

 or half-seconds in order to determine the rate of pulsation. 



(a) Determine the frequency of the beat at the room tempera- 

 ture, making a note of the temperature of the room. 



(6) Bathe the heart for several minutes with o.6-per-cent XaCl 

 solution warmed to 37 C. Allow the drum to revolve again at the 

 same speed as before, recording the second tracing under the first 

 one so that a comparison may easily be made. 



(c) Bathe the heart again with salt solution at the room tem- 

 perature. Continue the bathing with salt solution cooled in an ice 

 bath to 5 C. Make another record, under the first two, together 

 with a time tracing. 



How do (a), (6), and (r) compare in the number of beats per 

 minute? 



