128 



NA TURE 



YJiine 1 8, 1874 



change of form and arrangement, which Mr. Darwin has 

 described as " aggregation."] 



2. The image reflected by the mirror of a Thomson's 

 galvanometer having been thrown on the screen near its 

 right edge, it was first shown that when a fraction of a 

 voltaic current passed through the electrodes in a direc- 

 tion from the lecturer's right hand towards his left, the 

 spot on the screen moved towards the left of his audience, 

 The galvanometer having been shut off, a muscle was 

 placed on the electrodes with its cut surface against the 

 left (6-') electrode, and its natural surface against the right {c). 

 On again connecting the electrodes with the galvanometer 

 the spot flew off in the same direction as before. 



3. The nerve of the muscle having been placed across 

 two wires in connection with the ends of the secondary 

 coil of a Du Bois' induction apparatus, was excited by 

 induced currents, the muscle remaining on the electrodes. 

 The spot returned towards its original position. 



Fig. I. — Diagram of the experiments. — S, screen facing the audience : ' 

 position of electric light; G, reflecting galv, 

 edle and of the 



fi.ved to it : O. positio 

 rrent exists in the galv; 

 right; ff' his electrodes, 

 stalk J towards the \ 



the direction of thi 



the bright image on the screen when 



meter ; L, end of the lecturer's table 



which the blade of the leaf / rests, wi 



right ; 7('w', wires leading to the gal 



direction in which the current flows through the galvanometer wi 



leaf is in the position shown. The arrow near O indicates the di 



in which the spot of light moves under the 



[In both of these experiments only one-tenth of the 

 muscle-current was allowed to pass through the galva- 

 nometer. The electrodes used, which are constructed on 

 the same principle as those of I)u IJois-Reymond, are 

 shown in Fig. 2. The glass U-tubcs A A' are half 

 hlled with saturated solution of sulphate of zinc. The zinc 

 rods 15 B' are in metallic connection with the galvanometer 

 ends by the wires W W. The ends by which they dip 

 into the solution are carefully amalgamated. The straight 

 tubes C C are of such width that they slip easily into the 

 mouths of the U-tubes : they are prevented from going too 

 far by rims of sealing-wax. These tubes are filled with a 

 paste made by rubbing up modelling-clay with one per 

 cent, solution of common salt. The electrodes are so 

 supported that their distance and relative position can be 

 varied with great facility.] 



4. The heart of a frog was then placed with its apex 

 against the left electrode (c') and its base on the right (<■)■ 

 The spot moved in the same direction as before, but each 

 heart-beat was marked by a sudden return of tiie needle 



towards its original position, indicating the instantaneous 

 disappearance of electromotive force in the act of contrac- 

 tion. The etfect corresponding to the contraction of the 

 auricles could even be distinguished from that of the 

 ventricular contraction which succeeded it. 



5. A leaf of Diona:a, with its leaf-stalk still attached, 

 was placed with its stalk end on the left electrode and its 

 point on the right, as in Fig. i. The direction of move- 

 ment was the same. 



6. The spot having assumed a fixed position on the 

 screen, the leaf was excited by touching the sensitive 

 hairs with a camel-hair pencil. The spot flew back to- 

 wards the right edge of the screen, immediately afterwards 

 returning to its original position. This eftect was repeated 

 several times. 



7. The leaf-stalk was cut off, the leaf remaining as 

 before on the electrodes. The deflection was increased 



r<^ w 



Fig. 2. — Non-polarisable electrodes £ 



xperiments on the Dion.-ea 



(more than doubled). It was then explained that when 

 the leaf- stalk is itself placed on the electrodes, the gal- 

 vanometer indicates the existence of a current opposed in 

 direction to that of the leaf, showing that the electrical 

 conditions on opposite sides of the joint between stalk 

 and leaf are antagonistic to each other. Consequently, 

 so long as leaf and stalk are united, each prevents or 

 diminishes the manifestation of electromotive force by 

 the other. This is completely in accordance with what is 

 observed with reference to nerve, and is known as " elec- 

 trotonic variation of the nerve current." 



8. Two fine pointed electrodes, each in connection with 

 one end of the secondary coil of the induction apparatus, 

 were thrust into the centre of the external surface of a 

 leaf, the ends of which rested on the electrodes of the 

 galvanometer. On thus exciting the leaf the spot of light 

 shot to the left, but it was observed that there was an 

 obvious interval of time between the excitation and the 

 effect. This period, though of much greater duration, 

 corresponds to the so-called "period of latent stimula- 

 tion " in muscle. 



The plants exhibited and used for the experiments were 

 provided by the kindness of the Director of the Royal 

 Gardens, Kew. 



