1907.] during the Natural Beat of the Frogs Heart. 325 



(/). The successive events comprise an initial rise at (b) (negativity of the 

 base), then a sudden fall at (c), occurring 0"*04 later ; this gradually ceases, 

 and after some little time a final or terminal rise (negativity of the base) recom- 

 mences at (e). Such a record indicates that the base activity, commencing at 

 (b) and beginning to subside at (/), is maintained longer than the apex 

 activity which commences at (c) and begins to subside at (e) ; the duration of 

 the base activity in this case was 1" # 24, that of the apex activity was 1"'08. 

 The curve is in all essentials similar in character to that already referred to as 

 obtained from the mammalian heart in situ, both the first, or initial, phase and 

 the second, or terminal, phase having the same sign. Similar records of less 

 extent were obtained when the contacts were appropriately placed upon the 

 external body wal] of the frog without exposing the heart, whilst similar 

 ones of larger extent were obtained when the pericardium was opened and 

 the contacts placed upon the actual cardiac surface. If the heart is excised, 

 then the records gradually change in character until ones of the character 

 shown in fig. 1 may be obtained ; these correspond in type with those described 

 by Burdon-Sanderson as obtained from the immobile excised heart aroused 

 by an artificial stimulus. It is, however, certain that the diphasic effect with 

 phases of opposite sign, such as that shown in fig. 1, is not characteristic of 

 the frog's heart when examined in situ, supplied with blood and beating 

 naturally. 



An interesting modification in the type of the records occurs if the 

 ventricle is distended with blood; such distension is readily produced by 

 slight pressure upon the vessels leading from the truncus arteriosus. In 

 order to obtain the modification, the contact upon the groove is now so 

 placed as to comprise that portion of the ventricle base which lies near the 

 exit of the aorta. The modification is shown in fig. 3, which gives one full 

 ventricular change. At the point (h) the base negativity due to activity of 

 this part commences, the rise is cut short, as before, at the point (c), 0"'05 

 later, this being due to the propagation of the active state from the base to the 

 apex and the commencement of the apex change ; the apex change is, how- 

 ever, itself now cut short at the point (d) by a third change occurring about 

 0"*05 later, and this last change is of the same type as. the initial base one, 

 i.e., indicates a second development of base negativity. On the subsidence 

 of the apex effect, which begins at the point (e), these two more prolonged 

 base effects, being in the same direction, are summated and produce the con- 

 spicuous terminal phase which culminates at the point (/). There is no 

 doubt that the period from (b) to (c) indicates the time taken by the wave 

 of activity in its propagation from the base to the apex, in this instance 

 (temp. 12° C.) at a rate of from 130 to 140 mm. in 1 second: it follows that 



