232 Mr Langley. Central nervous system of the frog, [Mar. 10, 



converge to a root, real or imaginary, of the equation / {u) = 0. 

 Representing as usual the imaginary value f, = a? + iy, by means 

 of the point whose co-ordinates are x, y, and in like manner 

 ^^, = x^-\-iy^ &c. ; then we have a problem relating to an infinite 

 plane; the roots of the equation are represented by points A,B, C,...; 

 the value ^ is represented by an arbitrary point P ; and from this 

 by a determinate geometrical construction we obtain the point Pj, 

 and thence in like manner the points P^, Pg... which represent the 

 values f^, fjj ?3--- respectively. And the problem is to divide the 

 plane into regions, such that starting with a point P^ anywhere in 

 one region we arrive ultimately at the root A ; anywhere in 

 another region we arrive ultimately at the root P; and so on for the 

 several roots of the equation. The division into regions is made 

 without difficulty in the case of a quadric equation, but in the 

 next succeeding case, that of a cubic equation, it is anything 

 but obvious what the division is, and the author had not succeeded 

 in finding it. 



March 10. 1879. 



Professor G. D. Liveing, President, in the Chair. 



Mr J. R. Harris, Fellow of Clare College, was ballotted for and 

 duly elected a FelloAV of the Society, and Mr C. T. Haycock, 

 Exhibitioner of King's College, was ballotted for and duly elected 

 an Associate of the Society. 



The following communication was made to the Society: — 



Mr J. N. Langley, M.A., A preliminary account of some 

 phenomena of the central 'nervous system of the frog. 



The experiments were made on frogs without cerebral hemi- 

 spheres ; the reflex time was at first determined by Tiirck's method, 

 but this containing many sources of error, a fresh method was later 

 devised with these sources of error as much as possible done away 

 with. The section of either the sciatic nerve, or the cutaneous 

 nerves running to. the skin of the back, or of the brachial nerve, 

 caused an increase in the reflex time of the leg with the intact 

 sciatic. So far as the experiments went, the effect was greatest 

 when the sciatic was. cut. The effect might be due either to 

 a stimulus causing inhibition set up by the section or by the 

 section removing impulses previously causing inhibition. The 

 latter probably is the case, since in the preliminary exposure of the 

 nerve there is no increase of the reflex-time but usually a diminu- 

 tion, and since weak stimulation of the cut dorsal cutaneous 



