LIV.] 



SUSPENSION METHODS FOR HEART. 



269 



points of the two levers. Moisten the heart from time to time 

 with serum or dilute blood. 



(e.) After obtaining a tracing where the auricle and ventricle 

 contract alternately (fig. 192), screw up the clamp slightly until 

 the ratio of auricular to ventricular contraction alters, i.e., until, 

 by compressing the auriculo-ventricular groove, the impulse from 

 the auricles to the ventricle is " blocked " to a greater or less 

 extent, when the auricles will contract more frequently than the 

 ventricle. 



4. Excised Heart (Gotch's Arrangement). 



By this method all the parts are fixed to a f-piece which is 

 clamped in a stand, so that the whole, preparation, electrodes and 

 everything, can be easily adjusted (fig. 193). 



Fio. 193. Gotch's Arrangement for Excised Heart. All parts are fixed on one T-plece, 

 T.P. F. Clamp-forceps for heart ; C. Cork ; L. Lever. 



(a.) Excise a frog's heart, suspend it by clamp-forceps (F) to a 

 horizontal rod attached to a f-piece (T.P.). On the f-piece is 

 a cork into which the electrodes are fixed, while the heart pulls on 

 a counterpoised lever. 



(b.) By means of this arrangement we can (i) with a Stannius 

 heart show (i.) the latent period of cardiac muscle or cardiac delay, 

 (h.) the delay of transmission of an impulse from auricle to 

 ventricle in the groove; (2) with a beating heart, the refractory 

 period, rhythm, inhibition from the sinus (crescent), effect of 

 atropine, muscarine, &c. 



5. Place a frog on a crank-myograph, attach the apex of the 

 heart still in situ to the crank-lever and record its movements. 



