1880.] Dr. J. Burdon- Sanderson. On a New Rheotome. 383 



subsides, but very slowly. The nearer the wire, and the longer it 

 remains hot, the greater the electrical difference produced, and the 

 longer the time required for its subsidence. Corresponding results are 

 obtained by touching the surface, in the manner before described, 

 with a camel-hair pencil, containing solution of common salt. The 

 immediate result is to render the surface so acted upon positive to the 

 other surface. Here, as before, the effect rapidly subsides. If now, 

 the application is repeated or a stronger solution is used, the first 

 effect is the same, but it is followed by a slow deflection of the needle 

 in the opposite direction. 



It is important to notice that, in both modes of acting on the 

 surface of the ventricle, the primary effect (that of increased " posi- 

 tivity " of the warmed or slightly injured surface) is, when measured 

 in electromotive force, inconsiderable. After warming, we have never 

 observed a greater difference than 0'003 volt. When the solution of 

 salt is used the effect may amount to as much as 0*001 volt. The sub- 

 sequent negative effect varies according to the extent and degree of the 

 injury, and may, as stated in our former paper, amount to from two to 

 three hundredths of a volt. 



Another question relating to the physiological condition of the 

 resting heart is that of the influence of temperature on its excita- 

 bility. "We have estimated the excitability of the ventricle by measur- 

 ing, at different temperatures, galvanometrically, the strength of the 

 weakest induction shock by which a response could be evoked, and 

 have arrived at the general result that, when the temperature is raised 

 from 10° C. to 30° C, the excitability increases by one- third or one- 

 sixtieth for each degree. The suggestion offers itself that the two 

 new facts which have been stated, viz., the slight positivity of the 

 warmed surface and the increased excitability are correlated, but it is 

 of no value, excepting as an indication for further experiments. 



The full account of the experiments, of which the results are shortly 

 communicated above, will be published in the "Journal of Physiology." 



II. "On a New Rheotome.*' By J. Burdon-Sandersox, M.D., 

 LL.D., F.R.S., Jodrell Professor of Physiology, University 

 College. Received May 5, 1880. 



I beg leave to submit to the Royal Society the following description 

 of an instrument intended for the purpose of investigating the succes- 

 sive phases of the electrical change which takes place in the excitable 

 parts of plants and animals in consequence of excitation. Two instru- 

 ments intended for a similar purpose are already in use. One of them, 

 known as the differential or repeating rheotome, was devised by Pro- 



