456 



Drs. T. L. Brunton and T. Cash. 



by a longer pause than usual, which compensates for the diminished 

 interval between the two first beats. Sometimes no ventricular con- 

 traction is induced, and then instead of acceleration there is apparent 

 inhibition, the application of the stimulus being followed simply by 

 a longer diastolic pause than usual. 



Marey's observations were confined entirely to the movements of 

 the ventricle, but we have extended ours to the movement of the auricle 

 as well. We employed two levers : one resting upon the ventricle, 

 and the other upon the auricle, which recorded movements upon a 

 revolving cylinder covered with smoked paper. 



It is unnecessary to enter here into a fuller description of the 

 apparatus, which is given elsewhere.* 



By the method employed we are able to study the effects of maximal 

 and minimal stimulation applied to the ventricle, auricle, and venous 

 sinus upon the movements both of auricle and ventricle. 



By minimal stimulation we understand the smallest shock that pro- 

 duces any visible effect that in any way modifies the course of cou- 

 traction or the rhythm of the organ ; and by maximal stimulation we 

 mean the electrical irritation of such a strength that its intensification 

 produces no visible increase in its effect. 



The apparatus for stimulation consisted of a bichromate battery 

 with two zinc (3^ inches by 2 inches) and three carbon plates, the 

 size of these being 8 inches by 2 inches. This was connected with a 

 coil, and a key was interposed by which the primary circuit could be 

 made and broken at pleasure. The moments of opening and closing 

 the circuit were registered upon the same revolving cylinder as 

 that upon which the cardiac pulsations were noted, by means of an 

 electro-magnet, the marker of which was placed immediately under 

 the pens of the cardiac levers. In all the tracings the upper curved 

 line shows the ventricular contractions, the lower curved line the 

 auricular contractions, and the broken straight line the moment of 

 excitation. The descent of the line indicates the opening, the ascent 

 the closing of the current. 



In the secondary circuit were placed the electrodes for stimulating 

 the various parts of the frog's heart, and this circuit also could be 

 broken or changed at pleasure by means of an interposed double key. 



The heart was stimulated by a single induction shock. In 

 minimal stimulation only the breaking shock was effective, in 

 maximal stimulation both making and breaking shocks. The appa- 

 ratus, which is described in a separate note, admitted of the venous 

 sinus, auricle, or ventricle being stimulated at will. 



When recording the effects of stimulation of the venous sinus we 

 speak only of changes in rhythm of auricle and ventricle. 



We shall examine seriatim the results of irritation of each of these. 

 * Cash. "Journal of Physiology," vol. iv, No. 2. 



