326 MESSRS. F. GOTCH AND V. HORSLEY 



The absolute values obtained in the electrometer varied in the two stages, as 

 estimated by the eye, and the rough estimate thus formed is supported by the better 

 evidence of the photographs. They average 2 divisions, rarely 3 divisions for the 

 tonic stage, and 1 '5 divisions for the clonic stage. 



It would appear that this is true for the Carnivorous animal, as represented by the 

 Cat (eleven animals observed). Whether these electrometer figures are the same for 

 the Monkey we are unable to say, as we devoted our attention in the experiments on 

 that higher Mammal (seven animals observed) to photographing the results. 



The absolute electromotive values obtained by the electrometer and recorded photo- 

 graphically, are being examined by Mr. G. F. BUECH at the present time, and we, 

 therefore, will postpone the further consideration of this most important point. 



(b.) Effects seen in the Galvanometer. 



The total effect produced in the galvanometer when it is connected with the spinal 

 cord, and the cortex is excited, resembles the records of the muscular contractions, in 

 that there are two distinct stages. It need, however, hardly be said that the slow 

 swing of the galvanometer needle is incapable of recording intermittently, and con- 

 sequently both stages are composed of a series of summated effects. The rate of 

 movement of the needle is notably different in the two stages, and the close observa- 

 tion of this feature proved of much value in other experiments, notably those on the 

 corona radiata, see p. 337. 



In the first stage the needle generally begins to move soon after the commence- 

 ment of the cortical excitation (see Method, p. 299), but often owing to one of the 

 depressing circumstances mentioned on p. 272, the cortex is not normally excitable and 

 the effect it produces when stimulated is consequently delayed. The needle swings 

 steadily during the excitation, but when this ceases there is a distinct check,* and 

 then as the after-effect develops the needle slowly swings on and gradually comes to 

 a standstill at the end of the second stage or after effect. The mode of termination 

 of this last is slow and deliberate in its gradual diminution, thus contrasting markedly 

 with the abrupt cessation of the galvanometer excursion, when the corona radiata or 

 spinal cord is excited. This gradual dying out of the effect is so absolutely 

 characteristic of the cortex that it can be used for differentiation. 



Though well aware of the small value to be attached to the quantitative use of the 

 galvanometric readings thus obtained, we venture to add a few remarks on these in 

 view of the novelty of the point. 



When the central end of the whole cord is connected with the galvanometer, and 



* What is said on p. 299, &c., relating to possible errors and fallacies may be here remembered as 

 showing that this check is purely a physiological phenomenon, there being no possibility of the excitation 

 current affecting the delicate galvanometer. 



