380 Dr. J. Burden-Sanderson and F. J. M. Page. [May 13,. 



diminished excitability, during which it will not respond to a shock of 

 the same intensity. This he termed the "refractory period;" he 

 further found that if the induction shocks were strengthened, a 

 second response could be obtained after a shorter interval, but that 

 in this case the interval between excitation arid response was 

 increased. 



For the purpose of obtaining information as to the time-relations of 

 these phenomena, we adopt the following method : — For one of the 

 wires leading from the battery to the primary coil of the du Bois 

 induction apparatus, two are substituted, of which one passes through 

 the ceutral, the other through the peripheral pools of the rheotome. 

 The primary circuit is thereby closed, and immediately afterwards 

 opened twice in each revolution ; the intervals between the two excita- 

 tions can be varied at will. The closing shocks being cut off in the 

 way before mentioned, the rheotome is set so that the two opening 

 shocks follow each other at an interval of two seconds. If the ven- 

 tricle is at 10°C, and the distance of the secondary from the primary 

 coil such that the excitation is just sufficiently strong to produce a 

 contraction, it is usually followed by a second. If the interval between 

 the two excitations is shortened by the tenth of a second, the second 

 excitation is fruitless. If now the temperature of the preparation is 

 increased by a single degree, a response occurs which in its turn is> 

 abolished by taking another tenth off the time interval, and so on. 

 Proceeding in this way we obtain the clearest possible demonstration 

 of two facts, namely, (1) that the duration of the period of diminished 

 excitability agrees pretty closely with that of electrical activity, and 

 (2) that it is similarly affected by changes of temperature. 



5. Rate of Propagation of the Excitatory Wave. — It has already been 

 stated that the rate of propagation of the " Reizwelle," i.e., of the 

 excitatory electrical disturbance, was estimated by Engelmann to be 

 50 millims. per second. His observations, indeed, give a less rate 

 than this, but for good reasons, which he has stated, he thinks that 

 they require correction. We have been able by the following method 

 to show that the estimate is considerably below the mark. The heart 

 is led off as usual at the base (/) and near the apex (m), and excited 

 at the apex (x), and care is taken that the contacts x, m, and/ are in 

 the same straight line. A third non-polarisable electrode is in con- 

 tact with the surface at m between m and /, and 4 millims. 

 from to.* The time after excitation, at which, the first effect, i.e.,. 

 the first negative deflection is observed, is determined at to and m' r 

 by rheotome observations, in which the galvanometer circuit passes 

 through to and to' alternately (for which purpose a switch is used). 



* These measurements could not have been carried out had we not possessed a 

 few gigantic specimens of R. esctdenta, from the Platten See in Hungary. These 

 we owed to the kindness of Professor G-oltz. 



