March 21, 1889] 



NATURE 



501 



belonging to Dr. Burdon Sanderson, who kindly placed it at our 

 disposal. This instrument, when the capillary was magnified 400 

 times by the observing microscope, gave a perceptible response 

 when connected through a resistance of 10,000 ohms for one- 

 thousandth of a second with an electromotive difference of only 

 0003 D. The amount of movement of the mercury was estim- 

 ated by the divisions of a micrometer eye-piece, one division of 

 which indicated an actual movement of ^Jir of a millimetre. 

 After we had found that the electrometer, when connected with 

 the transverse and longitudinal surfaces of the sciatic nerve of the 

 toad, showed a response of one division following the application 

 of a single stimulus, whether electrical or mechanical, we 

 proceeded to the examination of the sciatic nerve in the rabbit, 

 cat, and monkey. For these experiments the animal was in 

 every case kept under the influence of ether, which was main- 

 tained throughout the whole experiment, and the animal was 

 killed before recovery. The sciatic nerve seemed for many 

 reasons the most suitable of the mammalian nerves. It can be 

 quickly prepared for 7 or 8 cm. of its length, its nutrition is well 

 preserved, since the arteria comes nervi ischiadici can be left 

 uninjured, and its diameter lessens the dangers of drying. 



The nerve, having been rapidly prepared and bathed in warm 

 saline solution, o-6 per cent., was ligatured low down in the thigh, 

 the ligature including the popliteal trunks. It was then divided on 

 the peripheral side of the knot, and raised in air so as to be at 

 right angles to the limb. One kaolin pad of a non-polarizable 

 electrode was applied to the cut end, and another to the longi- 

 tudinal surface at a distance of i "5 cm. A pair of sheathed 

 exciting platinum electrodes, 2 mm. apart, was then applied to the 

 trunk of the nerve 6 cm. centrally from the nearest leading-off 

 electrode, i.e. opposite the sciatic notch. The exciting stimulus 

 was obtained by the break of the current of a-single Callaud cell 

 supplying the primary coil of a du Bois-Reymond inductorium 

 graduated by Kronecker. The break shock produced in the 

 secondary coil by this means was so feeble as to be barely 

 perceptible on the tip of the tongue when the secondary coil 

 completely covered the primary. The break was effected by 

 the spring rheotome, which opened a fixed key at a definite 

 point in its course. The electrometer was connected with the 

 non-polarizable electrodes by a circuit which included the usual 

 compensator. By means of a switch the electrometer could be 

 cut out, and the circuit made to include a high resistance gal- 

 vanometer, which also revealed the single variation. The two 

 instruments could be thus readily compared. The excursion of 

 the mercury of the electrometer was ascertained both by direct 

 observation in terms of the divisions of the micrometer eye-piece, 

 and by photographing the projected capillary upon a moving 

 sensitive plate ; in the latter case the capillary was magnified 

 100 times. The results of our observations are briefly as 

 follows :— 



The mammalian nerve showed a well-marked difference or 

 demarcation current— that is to say, the electrode upon the longi- 

 tudinal surface was notably positive to that on the cut end. The 

 movement of the mercury corresponding to this difference 

 amounted in some cases to 60 divisions of the micrometer, 

 and was produced by an electromotive force which was estimated 

 as from about o'oi to 0-015 D. The passage of the single 

 break induction shock through the platinum electrodes in either 

 direction was followed by a small quick movement of the mercury, 

 which was invariably in the opposite direction to that produced 

 by the demarcation current. Its amount varied in difi"erent 

 animals from i to 2*5 divisions of the micrometer eye-piece, and 

 was photographed. After severing the nerve from the bulbo- 

 spinal system above the exciting electrodes, the same effect was 

 obtained ; its character, as shown by the movement of the 

 mercury, was, however, different, being as we believe much 

 shorter in duration and less in amount. But, our experiments 

 not being directed to the elucidation of this point, we will not 

 spe.ik positively with regard to it. After a time, varying in 

 different cases from twenty minutes to three-quarters of an hour, 

 the effect was no longer visible. We convinced ourselves that 

 the movement we obtained and photographed was due to the 

 electromotive change which accompanies the propagation of an 

 excitatory state along the mammalian nerve when this state is 

 evoked by the application cf a single stimulus. 



Part II. Excitation oj the Cortex Cerebri. 

 A. Mixed Spinal Nerve connected with the Electrometer.— In 

 two cases we have connected in the manner described in Part I. 

 the sciatic nerve with the electrometer, and have then exposed 



by a small trephine opening the so-called motor cortical centre 

 for the lower limb. This we then excited by a very weak but 

 adequate faradic current. So far, however, we have not been 

 able to detect any movement in the mercury, although the 

 muscles of the investigated limb supplied by the anterior crural 

 nerve were thrown into a state of active convulsion. It is prob- 

 able that the character of the neural disturbances in the mixed 

 nerve may be best studied by investigations which we shall 

 shortly undertake upon the electromotive changes in the 

 muscles. 



B. The Spinal Cord connected with the Electrometer. — The 

 experiments, the results of which are now to be briefly detailed, 

 were made in the following manner : — 



The spinal cord of the etherized animal (cat and monkey) was 

 exposed in the lower dorsal region for about 4 cm., and as low 

 down as the upper end of the lumbar enlargement. Great care 

 was taken by bathing with warm saline to guard as much as 

 possible against the dangers of error due to cooling and drying. 

 The dura mater having been split longitudinally, a strong thread 

 was passed round the spinal cord at the lower limit of the part 

 exposed. It was tied firmly and the cord divided below the 

 knot. By successive division of the two or three roots exposed 

 in the intervertebral foramina, the cord was easily raised from 

 the neural canal and suspended in the air without any great 

 interference with the circulation in the longitudinal vessels. 



One of the non-polarizable electrodes was then brought into 

 contact with the cut end of the cord and the knotted ligature, 

 while the other was connected with the longitudinal surface of 

 the cord 2 cm. from the cut end by means of soft thread cables 

 soaked in saline solution and tied loosely round the cord. In 

 one experiment the connection was with one lateral column only. 

 Mass movements of the electrodes upon the spinal cord were 

 suitably guarded against, though it was found that the cord 

 might be shaken without producing any effect in the electro- 

 meter. 



On connecting these electrodes with the electrometer a con- 

 siderable electromotive difference was found to exist between 

 the contacts, the excursion of the mercury being so great, i.e. 

 beyond the field of the microscope, that its amount could not be 

 estimated in terms of the micrometer eye-piece. The cut surface 

 was always negative to the longitudinal surface, and the amount 

 of the difference as estimated by the compensation method was 

 about o'02 D. It appeared to be highest when the section 

 passed through the dorsal region without involving the lumbar 

 enlargement. A difference between the surfaces of the cord 

 has been previously observed by du Bois-Reymond, 



The cortex cerebri was now exposed and the exciting circuit 

 prepared. The inductorium previously employed was again 

 used with one Daniell cell in connection with the interrupter of 

 primary coil and the Helmholtz side wire. The exciting elec- 

 trodes had platinum points 2 mm. apart. 



The demarcation current having been compensated, and the 

 electrometer placed in connection with the non-polarizable 

 electrodes, the motor area for the lower limb was excited. The 

 results of the observations made upon four monkeys and several 

 cats may be summed up as follows : — 



(i) The application of the exciting electrodes to the cortex 

 was without exception only followed by a movement in the 

 electrometer when the area of representation of the lower limb 

 was touched, and this even when owing to prolonged excitation 

 of the arm area the upper limb was in violent epileptic convul- 

 sion. We found that when the exciting electrodes were moved 

 over the surface of the brain the observer at the electrometer only 

 gave notice of a movement in the instrument when the person 

 exciting had crossed the margin of representation of the limbs. 

 This shows that electromotive changes in the cord sufficient to 

 affect our instrument occurred only when the motor area of the 

 lower limb was excited. All error due to escape is thus set on 

 one side, while at the same time this remarkable fact confirms 

 the localization of function. 



(2) The excitation of the motor area for the lower limb was 

 accompanied and followed by characteristic movements of the 

 mercury. The excitation by means of the interrupted current 

 usually lasted for three seconds — that is, about 300 equal and 

 alternately directed induction currents passed through the excited 

 tissue. During this period the mercury showed an excursion 

 opposed in direction to that of the difference between the 

 longitudinal surface and cut end of the cord. This excursion 

 persisted as long as the excitation lasted, and ceased when this 

 was left off. Then after an interval of from one to three seconds 

 there ensued a rhythmical succession of excursions each opposed 



