446 



THE PROPERTIES OF STRIPED MUSCLE. 



than the other, or by bringing near to the surface which it is desired to 

 warm, a minute coil of platinum wire, heated to any required amount 

 by leading a battery current through it. By the first method it may be 

 shown that a very slight difference of temperature between the apex 

 and base of the ventricle is sufficient to alter the character of the 

 variation. If, with the proximal contact on the former and the 

 distal on the latter, the temperature of the apex is slightly raised, 

 the effect shows itself in the strengthening of the terminal phase, 

 and shortening of the isoelectric interval. The second method has the 

 advantage that it enables us to localise the action of warmth with more 

 exactitude, and to prove that, whether the contacts are on the opposite 

 sides of the ventricle, or at opposite ends, the electrical response of the 

 unwarmed contact to stimulation is always greater than when both 

 contacts are at the same temperature. It is further found that, in the 

 absence of excitation, a warmed surface becomes slightly positive to an 

 unwarmed, the amount of difference of potential, however, not exceeding 

 toW °f a v °lk, an( l soon giving way to an effect in the opposite 

 direction. 



The excitatory variation as observed by the capillary electro- 

 meter.— Two years later, the rheotome results above described 



were verified and extended by this method, 

 which was then new. 1 A large number of photo- 

 graphic records were taken, relating to the ven- 

 tricle of the heart of the frog and of the tortoise, 

 in which the time-relations of the excitatory 

 variation were fully demonstrated. The character 

 of the results can be best understood by the 

 following series of tracings (Fig. 249), copied 

 from photographs made in August 1882 : — 



No. 1 represents the normal variation of the 

 ventricle of a Stannius preparation excited 

 from the auricle, with the proximal leading-off 

 electrode at the base, the distal on the apex. 

 Period of latency, - 45 sec. ; interval between 

 first and second phase, 1*4 sec. 



No. 2. The same with the apex devitalised 

 by heat. 



No. 3. Uninjured ventricle, leading-off elec- 

 trodes as before ; excitation at the apex close to 

 what was before the distal contact. 



No. 4. The same ; the now proximal contact 

 warmed by a platinum coil placed at a distance 

 of 3 mm. from the surface. 



No. 5 shows the actual differences of poten- 

 tial during the two phases of the variation 

 represented in No. 1, as deduced from more 

 recent photographs obtained with a more sensit- 

 ive instrument. The first phase corresponds, 

 both as regards differences of potential and time- 

 relations, to Engelmann's curve, published in 1878, 2 representing 

 the mean result of thirty-three observations of the variation in the 



1 Sanderson & Page, Journ. Physiol., Cambridge and London, vol. iv. p. 327. 



2 Engelmann, Arch. f. d. ges. Physiol., Bonn. Bd. xvii. S. 68. 



Fig. 249. 



