107 



353. Action of Drugs on Heart. The experiments 

 may be performed upon a heart which has been removed and 

 placed in a watch-glass or preferably upon the heart in its 

 natural position. 



Muscarine. Pith a frog-, expose its heart and with a fine 

 pipette apply a drop of serum or normal saline solution con- 

 taining a trace of muscarine, which rapidly arrests the rhyth- 

 mical action of the heart, the ventricle being relaxed, i. e., 

 diastole, and distended with blood. Get a tracing from the 

 heart while under the influence of muscarine. 



Atropine. Remove the solution of muscarine as much as 

 possible by absorbing it with filter paper and after a few min- 

 utes, with another pipette, apply a few drops of a 0.5% solution 

 of atropine sulphate in normal saline, the heart gradually 

 again begins to beat rhythmically. Get a tracing. 



Pilocarpine. In another frog arrest the action of the 

 heart by applying a few drops of a 0.5% solution of pilocar- 

 pine, and then apply atropine to antagonize it, and observe 

 that the heart beats again after the action of the atropine. 



Nicotine. Apply a drop or two of a 0.2% solution of 

 nicotine. Stimulate the vagus and note that it no longer 

 arrests the heart's action, but stimulation of the sinus venosus 

 does ; so that nicotine paralyzes the fibers of the vagus and 

 leaves the intracardiac inhibitory mechanism intact. 



XXIX 



In this exercise four styles of sphygmographs are available. 

 Each student should obtain a tracing of his pulse from these 

 instruments ; fix and preserve the records for comparison. 



354. Ludwig's Sphygmograph. With a soft pencil make 

 a mark upon the skin of the wrist at the point where the radial 

 pulse is most distinctly felt. Apply the instrument so that 

 the button rests upon the pulse. Use the armrest so that the 

 parts will remain steady. Adjust the instrument so that the 

 writing lever will move freely and give as large a curve as 

 possible. Take tracings on the revolving drum. Suspend 

 respiration for a few seconds and notice whether there is any 

 effect upon the pulse. 



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