1907.] during the Natural Beat of the Frog's Heart 327 



Tirn& & 



c 



h 



4. 



DESCRIPTION OF FIGURES. 



The curves given in the above figures are outlines of four photographic records of the 

 displacement of the capillary electrometer meniscus. On each figure a rise in the curve 

 indicates relative negativity of the tissue under a contact upon the auriculo-ventricular 

 groove ; all the curves are to be read from left to right. 



Fig. 1. — Excised frog's heart, contacts upon auriculo-ventricular groove and upon the 

 ventricle apex ; natural beats ; (a) auricular activity, (b) commencement of 

 ventricular activity at base of ventricle, (c) commencement of ventricular 

 activity at apex of ventricle, (/) summit of final ventricular phase. 



Fig. 2. — Frog's heart in situ, contacts as in fig. 1 ; (a) commencement of auricular 

 activity, (b) commencement of ventricular activity at base, (c) commencement of 

 ventricular activity at apex, (/) summit of final phase. 



Fig. 3. — Frog's heart in situ, but during or after distension with blood, contacts on 

 ventricle base near spring of aorta and on ventricle apex ; (b) commencement of 

 general base activity, (c) commencement of ventricular activity at apex, (d) com- 

 mencement of base activity localised to neighbourhood of aorta, (/) summit of 

 final ventricular phase. 



Fig. 4. — Frog's heart in situ, contacts on each side of base near groove, one on left side 

 remote from aorta, the other on right side close to spring of aorta ; (a) com- 

 mencement of auricular activity, (6) commencement of activity under contact on 

 left side of base remote from aorta, (c) commencement of activity on right side 

 of base near aorta. 



before a similar change commences under the other contact, that is, in the 

 tissue near the aortic exit. The rise is, however, cut short at the point (c) 



