ON THE MAMMALIAN NERVOUS SYSTEM. 371 



being conditioned in the same general way as is the well-known electrical effect in the 

 excited Frog s nerve. 



As far as the galvanometer is concerned, since the falling time of our instrument 

 was 10 seconds, the effect for successive stimuli kept up for less than 10 seconds must 

 be obviously directly proportional to the time, hence, in all exact experiments involv 

 ing this instrument, it was essential that the duration of the period of stim illation 

 and the number, therefore, of the successive stimuli used should be the same. This 

 was effected by the revolving paraffin key described in Chapter III., which ensured 

 a strictly uniform period. 



(2.) Condition of the Animal. 

 A. AncKsthesia. 



The character of the effect in the cord, unlike that in the nerve, is varied not only by 

 the intensity of the stimulus, but also by the introduction of changes in the condition 

 of the animal. These are connected with the awakening of the central cellular 

 elements of the cord through the intensity of the stimulation used. The condition 

 of the animal largely affects the limit of intensity at which any stimulus becomes 

 adequate to arouse these corpuscular elements. Thus if profoundly anaesthetised a 

 strong stimulus is necessaiy, but if the narcosis be but slight, a weak stimulus may 

 evoke the result. 



Although the subject of anaesthesia has been already referred to in Chapter III., 

 it has such an important bearing on the present results that it must be reintro- 

 duced at this juncture. Our experiments abound with instances of the following 

 character : in a Cat (371) the lower (lumbar) end of the experimental tract was 

 connected with the galvanometer, and the lateral region of the cord in the upper 

 dorsal section was excited with a series of 500 successive equal and opposite induction 

 shocks (100 a second for 5 seconds). The galvanometric effect obtained was a 

 deflection of 230 scale, the anaesthesia though complete as regards consciousness 

 being of a comparatively slight character. The ether was now pushed and the 

 anesthesia made more profound, abolishing reflex movements, when the effect of a 

 precisely similar excitation was indicated by 142. 



In another animal (Cat 375) electrical effects similarly produced in a state of 

 profound and slight anesthesia show, when compared, the same differences, both with 

 minimal and maximal intensities of stimulus. 



