414 Sanderson and Page on Rhythmical Motions. [May 23, 



when two spots, 2 millims. apart, of which one has been injured, are 

 led off, nearly equal in amplitude those which are observed when the 

 contacts are respectively at apex and base. 



11. Decline of Effect after Injury. — The electrical difference between 

 an injured and a sound surface begins to decline from the moment of 

 the infliction of the injury which produces it. This decline is not 

 accompanied by a corresponding diminution of the variation, the 

 eventual decline of which is often preceded by a temporary increase. 



12. Modifications observed under the Influence of Radiant Heat. — By 

 warming the surface of the ventricle in the manner described in 7, 

 the following changes are produced in the character of the variation. 

 In the uninjured rhythmically contracting heart, in which the variation 

 has the normal character, the approach of the wire for five seconds to 

 a distance of 3 millims. from the surface of the auriculo-ventricular 

 groove intensifies the second phase and increases its duration. This 

 effect lasts for two minutes at most. It subsides at first rapidly — so 

 that each succeeding variation differs sensibly from the preceding one 

 — afterwards more gradually. 



If the apex be similarly warmed, the second phase is either oblite- 

 rated or reversed, according to the time of exposure and to the 

 distance of the coil. At first the variation assumes the characters 

 witnessed after injury of the apex, as described in 10 ; but here, as 

 when the base of the ventricle is warmed, the effects subside rapidly 

 during the first five seconds, more gradually afterwards. In both cases 

 the variation has, in about two minutes, resumed its normal characters. 



In the above experiments it is seen that, although the warming 

 influences the potential of the surface acted on in a direction which is 

 opposite to that produced by a permanent injury, its effect on the 

 variation is precisely the same, with this important difference, that it 

 is transitory. These effects can be observed whether the entire heart 

 or the ventricle alone is used. 



13. Modifications dependent on the Seat of Excitation. — If in the 

 entire heart, of which the motions have been arrested, either by 

 faradization of the inhibitory tract or by the Stannius' ligature, a 

 single contraction is induced either by a mechanical or electrical 

 excitation of any part of the auricles or of the auriculo-ventricular 

 groove, the excursions present the same characters as in the rhythmi- 

 cally contracting heart. If the excitation, whether electrical or 

 mechanical, be at the apex, the first phase of the variation is reversed, 

 i.e., the apex becomes initially negative. In other respects the ex- 

 cursion is unaltered. Consequently, if at the moment of excitation the 

 apex is warmed in the manner previously described in 12, the large 

 single excursion (apex-positive) is seen to be preceded by a momentary 

 prae-excursion in the opposite direction. 



