328 Electrical Changes during Natural Beat of Frog's Heart. 



by the commencement of such a change under the aortic base contact ; this 

 occurs in a number of measured records after a delay of from 0""06 to 

 0"'08, i.e., a longer interval than can be accounted for by the propagation 

 time from base to apex. Moreover, the base change which commences first 

 at (&), subsides first at (e), that commencing later at (c) subsiding later at (/), 

 and thus causing a second or terminal phase of opposite sign to the first, or 

 initial, one. Many records of this type have been obtained, and in every 

 instance the first phase is of the same character ; hence in the natural beat 

 the whole base does not pass simultaneously into the active state with its 

 associated relative negativity, the manifestation of such activity in the part 

 near the exit of the aorta being always delayed. 



The development of the frog's heart from a primitive S-shaped tube, and 

 the well-known fact that a contraction of the wall of the aortic bulb occurs 

 as the last stage of the whole cardiac cycle, are in accordance with the 

 observations now described. These show that the frog's heart, when fully 

 developed, continues to display signs of its ontogeny, and that even when 

 these are structurally imperceptible, they can be revealed by appropriate 

 physiological methods. 



[The experiments here described were all carried out upon winter specimens 

 of Bana temporaria during the months of January, February, and March.] 



