LABORATORY MANUAL OF PHYSIOLOGY. 



() Separate the auricles from each other. Record results. 



(/) If the ventricle has stopped beating, see if it will still re- 

 spond to mechanical or electrical stimuli. 



Draw conclusions from the above observations concerning the 

 mechanism of the heart-beat. 



EH. GRAPHIC RECORD OF THE FROG'S HEART-BEAT. 



Pith a frog. Pin, back down, on the frog board. Expose the 

 heart as in the previous experiment. The heart may be connected 

 with the heart lever by one of two ways. 



1. The Suspension Method. Make a small hook out of a 

 bent pin. Pass this through the tip of the ventricle, avoiding, if 

 possible, piercing the cavity of the ventricle. Attach this hook, by 

 means of a fine thread, to the short arm of the heart lever, placing 

 sufficient counterpoise upon the long arm to balance the weight of 

 the thread and pin and to raise the heart slightly from its bed. 

 Apply the writing point of the lever to the smoked paper of a 

 medium fast drum. Also, beneath the heart record, make a time 

 tracing in seconds. 



The auricular beat may be recorded separately, at the same 

 time, by attaching the auricle, in the same way, to another lever 

 which may be adjusted to write under or over the ventricle lever. 



2. Direct Transmission Method. An upright, made of 

 bamboo or some other light material, is attached to the long arm 

 of the lever nearer to or farther from the axis, depending upon the 

 magnification desired. The lower end of the upright is supplied 

 with a cork foot which may be made to rest upon the auricle or 

 ventricle. Every movement of the heart chamber upon which the 

 foot of the upright rests will be transmitted to the long arm of the 

 lever and will be recorded upon the revolving drum. 



By the use of either one of these methods record the contrac- 

 tions of the ventricles and auricles, noting the rate of pulsation and 

 the duration of each phase. Also note the form of the curve ob- 

 tained during systole. Compare systole with diastole. 



With the suspension method the ventricular record will prob- 



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