CONNPJCTED WITH THE BEAT OF THE MAMMALIAN HEART. 
181 
auricle ; when the auricle and ventricle contracted in sequence the variation was sS 
or indicating 
1. Negativity of auricle, viz., action of auricle. 
2. Negativity of leg, ,, ,, of ventricle apex. 
3. Negativity of auricle, ,, ,, of ventricle base. 
Observations 1 and 2 were defective, inasmuch as the leading-off electrode from 
mid ventricle was shifted between the two observations. 
Complementary experiment. —The animal was left in statu quo, and two hours later 
differences of potential were artificially established by pins inserted into the heart, 
through which were passed make or break induction shocks, or the direct current of a 
Daniell cell {vide fig. 4). The results were as follows :— 
With induced currents. (Make current from apex to base ; break current from 
base to apex.) 
Variations. 
Mouth to Hg. 
Leg to H2SO4 .... 
At make 
,, break 
S. 
N. 
Leg to Hg. 
Mouth to H.3SO4 
,, make 
,, break 
N. 
S. 
Leg to Hg. 
Heart near base to H3SO4 
,, make 
,, break 
N. 
S. 
Leg to Hg-. 
Heart near apex to H2SO4 
,, make 
,, break 
S. 
N. 
With the constant current. 
(Current from apex to base through heart.) 
Leof to Ho-. 
O O 
Leo- to Ho. 
Leg to Hg. 
Mouth to Hg. 
Mouth to Hg. 
On reversal of the current the 
Mouth to H^SO^ . 
Heart near base to H^SO^ 
Heart near apex to H0SO4, 
Heart near base to H0SO4 
Heart near apex to HgSO^ 
variations w^ere reversed. 
Variation at 
closure. 
N. 
N. 
S. 
N. 
S. 
The whole series of these variations was exactly as might have been anticipated. 
They were uniformly such as to indicate potential of the same sign in the vicinity of 
either pole as compared with the potential at more distant parts. It is worth again 
calling attention to the fact that potential at leg agreed with sign of pole at apex, 
while potential at mouth agreed with sign of pole at base, when the body was led off 
* It is often very difficult by inspection to distinguisb between suck variations; in the above case it 
was impossible to say whether the variation consisted of two movoraents in the same direction (sS), 01 - 
of two movements in the same direction separated by a movement in the opposite direction (snS) ; the 
latter is probably the correct reading. 
