ON THE MAMMALIAN NERVOUS SYSTEM. 483 



distal sides of the ganglion, they established reason for believing that the impulses 

 which affected respiration were delayed in transmission through the ganglion to the 

 extent of '036 second. As GAD and JOSEPH point out, these experiments are open to 

 the criticism that the summation of subminimal stimuli tnay be an important factor 

 in producing the result. 



C. The conditions under which the functional activity of the nerve centres of the 

 spinal cord, as indicated by muscular contraction, is evoked necessarily form the 

 major part of the facts at our disposal. 



These conditions may be arranged as follows : 



(l.) Adjuvants. Warmth. Preliminary influence of cold. After effects of section 

 of spinal cord* a little distance above the nerve centre. Some drugs, e.g., 

 strychnia, &c. 



(2.) Depressants. Prolonged fall of temperature. Shock after division of the spinal 

 cord (greater in proportion to proximity of section to nerve centre). t Anosmia. 

 Narcotic drugs (anaesthetics, &c.). 



(3.) Delay. A series of measurements have been taken of the time lost during the 

 passage of a nerve impulse from one posterior root through a spinal nerve centre to 

 the corresponding motor nerve of the same side. This delay, or time-loss, has been 

 estimated by the majority of observers! to be about '01 in the Frog. (ExNER, in 

 man, bulbar reflex '04 second). This refers only to the "direct reflex," i.e., of the 

 same side as the excitation. 



The delay with the " crossed reflex " (see later paragraphs) is '004 second longer 

 than the direct. 



(4.) Mode of Discharge. A spinal cord nerve centre can be excited by a single 

 induction shock if it be applied to an afferent channel. The effect produced as 

 recorded by the contraction of a muscle is apparently that of a single twitch. If an 

 interrupted current be applied to the spinal cord or an afferent channel, the effect 

 similarly recorded is a continuous contraction. 



An effect in the muscles of an intermediate form has been frequently recorded, viz., 

 a rhythm, the rate of which has been determined to be, on the average, eight to ten 

 per second. 



Occasionally an after effect has been noted, i.e., a few muscular responses after the 

 spinal excitation has ceased, and in some cases these are continuous. 



(5.) Trophism. It is well known that lesions of the spinal nerve centres which 

 involve the efferent nerves are attended by wasting and other evidences of failure of 

 nutrition in the parts which are in relation with the centre in question. 



* See FRANgois FRANCK, loc. cit. ; v. BEZOLD, loc. cit., &c., &c. 



t DE BOECK, ' Archiv fur d. ges. Physiologic' (confirmed also by our observations). 

 J Particularly HELMHOLTZ, WUNDT, FRANCK, CYON, and others. Loc. cit. 



3 Q 2 



