THE FROG HEART. 13! 



8. Action of the Constant Current on the Contractile 



Substance Of the Heart. For this purpose prepare electrodes as 

 directed in Exercise I. Fix a cork vertically on a sheet of lead about 

 an inch and a half square ; cover the top of the cork with wax mass, the 

 upper surface of which should be somewhat concave. Place the support 

 on a sheet of wet filtering paper and cover it with a beaker. Attach a fine 

 ligature to the frsenum, and remove the heart after severing the principal 

 vessels. Collect some blood and dilute it with as much 075 per cent, salt 

 solution, and place a few drops of it on the wax surface. 



Make a "ventricle-apex preparation," as directed in 6. Having ascertained 

 that it does not beat rhythmically of itself, fix it in its place by the aid of 

 fine glass pins and replace the beaker. 



Prepare and arrange two Grove's cells in circuit, interpose a key and a 

 pair of electrodes. Fix the electrodes, so that their points are in contact with 

 the apex and base respectively of the preparation. The passage through the 

 ventricle apex of a voltaic current in the direction of its axis produces 

 rhythmical action, which lasts as long as the current passes. 



9- Study of the Ventricular Systole by the Graphical 



Method. Prepare a writing lever consisting of a glass rod about ^ inch 

 in thickness and five inches long, having at one end a knob of glass, and at 

 the other a writing point. This is thrust through a square bit of cork, which is 

 then pushed up to the knob. A fine steel needle passes through the cork at 

 right angles to the rod. The rod also bears, close to the needle, a vertical arm 

 of cork, by means of which it rests on the ventricle. The preparation lies on 

 a metal plate, which forms the upper end of a cylindrical brass box, through 

 which water, at any desired temperature, can be passed. This plate is furnished 

 with bearings in which the steel axis of the lever works. The metal box is 

 fixed to one of the adjustable supports of the recording apparatus. 



a. The rhythmically contracting heart. 



Expose the heart as before. Raise it from the pericardium by a ligature 

 attached to the severed froenum, and cut through the vessels. Place the heart 

 on the plate, adding a few drops of dilute serum, and arrange the lever so that 

 the cork arm rests on the ventricle, and the writing end inscribes its move- 

 ments on the blackened surface of the cylinder. The rate of motion should 

 be about 20 inches per minute. 



Allow water at 12 C. to pass through the cylindrical box and record the 

 rhythmical contractions of the ventricle. Repeat the experiment, substituting 

 water at 17 and at 22, and compare the tracings. 



b. The curve of a single ventricular contraction. 



Prepare finely pointed electrodes as in I. I, arranging for single induction 

 shocks. Fix the electrodes to an adjustable support, so that they can be 

 brought with precision into contact with the preparation. Prepare a Stannius' 

 heart and arrange it for recording as in a. Adjust the electrodes, taking care 

 not to interfere with the lever. Place the secondary coil at about 10 centimeters 

 distance from the primary, or nearer, if on trial it is found necessary to do so, 

 Then bring the point of the lever into contact with the blackened paper, so 

 as to write a base line or abscissa, and open the key. The rate of motion 

 of the recording surface should be about 2\ inches per second. 



K 2 



