ON THE MAMMALIAN NERVOUS SYSTEM. 423 



excitability therein caused is in direct causal relation with the electrotonic effects of the 

 resting or persistent nerve currents produced between the cross section and the surface 

 of the nerve trunk. Since similar electrotonic alterations in excitability have been 

 shown to exist in the case of the spinal cord, it is most probable that a direct increase 

 would be produced by the very large resting currents which (see Chapter IV.) 

 have been found by us to be produced by cross sections of the cord. In this 

 connection we may draw attention to the following striking phenomenon described 

 by SCHFFF,* and which in the progress of the present research we have had the 

 opportunity of seeing ourselves. We often saw that after complete section of the 

 cord and the removal of a piece 1 centim. in length in the region of the 8th dorsal 

 vertebra, when the animal was asphyxiated on the completion of the investigation, a 

 sudden prolonged discharge of the nerve centres in the lower portion of the cord 

 occurred. This revealed itself by the rising up of the tail of the animal, and its main- 

 tenance in an erect position for one or two minutes. The discharge and its effect then 

 subside to be followed in two or three minutes by a second feebler one, and this by a 

 third still more feeble. In addition to this it often happened that during an experi- 

 ment on such a preparation, rhythmical discharges of the centres in the lower portion 

 of the cord occurred after the section, evidenced by rhythmical contractions of the anal 

 muscles. This has also been noticed by several investigators. 



Further, in one animal (Cat 325) in which the cord was divided at the 13th dorsal 

 vertebra, although the tail phenomenon did not spontaneously appear, when the 

 animal was asphyxiated, it was readily evoked in full strength by slight stimulation 

 of the skin of the tail. 



These phenomena afford a striking instance both of the hyperexcitable state of the 

 centres in the lower portion of the cord and of the capacity of these centres to 

 discharge such a series of nerve-impulses as will produce sustained co-ordinated 

 movements. 



The difficulties thus involved in the experimental methods of MIESCHER and WORO- 

 SCHILOFF are to a great extent obviated by experiments in which, a given lesion of the 

 cord having been made with all due antiseptic precautions, the wound has been 

 allowed to heal, and the animal examined carefully at varying intervals, from a few 

 days to weeks and months, after the operation. Such an experiment is that made 

 by FERRiERt on the Monkey, in which a hemisection at the level of the 8th dorsal was 

 followed by complete insensibility below, on the side opposite the lesion, to every 

 form of sensory stimulus, whilst the sensibility on the same side remained unimpaired. 

 This experiment is similar to the paralysis on the same side, and anaesthesia on the 

 opposite side, observed in some cases of injury or disease localised in one half of the 

 spinal cord. Other observers, notably MoTT,J have, however, obtained results which 



* SCHIFF, PFLUGER'S ' Archiv,' vol. 30, 1883, p. 202. 



t FURRIER, '.Brain,' 1884 



J ' Proceedings of the Physiological Society.' ' Proceedings of the Royal Society.' 



