80 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



upward. Allow the ventricle to register its cycles upon the smoked 

 paper of a slowly revolving kymograph above the record of a chrono- 

 graph beating once in every two seconds. What is the rate of the 

 heart per minute? Register the auricular beats in the same manner 

 after having previously inserted the hook in the wall of one of the 

 auricles. Note that the rhythm is the same in the two records, and 

 that the force of the contractions of the ventricle is much greater than 

 that of the auricles. 



Annotation. Very good records may also be obtained from the heart of a frog. 

 The animal is pithed in the usual way and fastened to a board by means of wire 

 clips. A median incision is then made through the skin over the sternum, and the 

 episternum raised with a pair of forceps. The edges of the sternum are cut through 

 and the bone removed in its entirety. The pericardium is then lifted up and divided, 

 thus exposing the beating heart. The sinus venosus of this heart is formed by the 

 union of the large inferior vena cava and the two smaller superior vense cavse. 

 It is continuous with the right auricle and ventricle. The latter continues as the 

 bulbus aorta?, which gives origin to the two aorta 3 . From the latter arise the pul- 

 monary arteries which supply the lungs. From here the blood is returned to the 

 left auricle, whence it is again forced into the ventricle. 



FIG. 50. RECORD OF THE CONTRACTIONS OF THE FROG'S HEART. 

 The time is registered in seconds. 



The registration may be effected in two ways, namely, by: 

 (a) The Supporting Method. A vertical rod of straw is fastened by means of 

 a thin wire to the long arm of an ordinary writing lever. The joint between them 

 should be very loose. The other end of this rod is made cup shaped by means of a 

 piece of wax molded to fit the surface of the ventricle. When the latter contracts 

 the lever is raised. Consequently, the systolic period is indicated by the up-stroke 

 and the diastolic period by the down-stroke of each wave. 



(6) The Suspension Method A fine thread is attached to the end of the short 

 arm of an ordinary writing lever. It is connected by means of a small hook with 

 the apex of the heart. The long arm of the writing lever is weighted sufficiently 

 to place a slight degree of tension upon the heart. In this case the up-strokes of the 

 record correspond to the systoles of the organ. If a spring lever is employed, the 

 tendency of which is to move upward, the string must be fastened to its long arm. 

 The contraction of the heart then pulls the lever downward, whereas the steel spring 

 attached to the lever pulls it upward as soon as the cardiac musculature becomes 

 passive during diastole. 



2. Effect of Temperature. Allow the ventricle to register its cycles 

 upon the paper of a slowly revolving kymograph. By means of a pipet 

 allow a few drops of iced saline solution (5 to 10 C.) to drop upon the 



