ON THE MAMMALIAN NERVOUS SYSTEM. 337 



(a.) Effects seen in Electrometer. 



The cortex and spinal cord having been exposed, the central end of the cord 

 divided in the lower dorsal region was connected with the instrument in the manner 

 already described, and the corona radiata displayed by the method detailed in 

 Chapter III., Section 2. 



We have already stated that it was early shown by FRANQOIS FRANCK and others 

 that removal of the cortex and excitation of the corona radiata no longer gave the 

 characteristic sequence of tonic followed by clonic muscular contraction, but simply a 

 tonic contraction synchronous with the duration of the excitation, the first stage, as it 

 were, of the cortical effect. In our earliest experiments (see Hoy. Soc. Proc. ), we 

 found that a similar difference occurred in the character of the electrical changes 

 observed in the spinal cord, as evidenced by the capillary electrometer. The character 

 of the change in the two conditions is well shown in the facsimile representations of 

 the photographic records which are given in our former paper, the corona radiata 

 effect being simply a persistent tonic negative variation, the amount of movement of 

 the meniscus being about one division of the eye-piece scale. 



The small size of the electrometer change, and the consequent difficulty of appre 

 ciating its comparative quantitative value under different circumstances, led us to 

 employ the galvanometer as an index of its amount. 



(b.) Effects seen in Galvanometer. 



When the effect in the cord is observed with this instrument it is seen to be unlike 

 that evoked by cortical excitation in this respect, that the deflection of the needle 

 commences with the application of the stimulus, and ends sharply with its termina 

 tion. The amount of the deflection is thus very definite, but of less extent than 

 that obtained when the cortex is excited. 



In the following table a series of observations made on three Cats are given, in 

 which precautions were taken to insure that the state of anaesthesia, &c., should be in 

 all cases as far as possible the same. The deflections vary from 37 to 175, the 

 average being 102. 



MDCCCXCI. B. 2 X 



