THE FROG HEART. l!40 



Follow the movement of the corpuscles, and practice singling 

 one of them out so as to follow its course from one end of the 

 measured length of capillary to the other. 



Adjust a 1/10 second record to write on a drum going at 

 a moderate speed, place a spring key in circuit, so that the 

 style vibrates when the latter is closed. 



Depress the key at the moment a corpuscle enters the 

 measured area, and release the key the moment that the 

 passage is completed. From the record estimate the rate per 

 second. 



In carrying out the experiment the co-worker should take 

 charge of the writing point, turning it on to the paper when 

 you are ready and off again each time a record is completed. 



The Frog heart. 



Required: Frog-heart recorder with parchment paper point tipped 

 with a glass filament, general stand, mductorium arranged for 

 interrupter shocks, light electrodes, 2 keys, and 7 wires. 



After pithing the frog plug the opening to arrest bleeding 



Lay the frog on its back on the frog plate, divide the skin 

 along the middle line for the length of the sternum without 

 opening the abdominal cavity. The sternum is then cut 

 through transversely, leaving a little of the cartilage below 

 undisturbed, and is then completely detached laterally and 

 above, care being taken in doing so to avoid injury to the 

 parts beneath. 



A window is thus made over the heart without opening the 

 pericardium or the abdominal cavity. 



Next open the pericardium, raise the heart with the glass 

 seeker and find the frenum on its dorsal aspect ; this contains 

 the small cardiac vein, divide it and turn up the heart. Note 

 the sinus forming the entrance of the large veins into the 

 risrht auricle. 



