54 NERVOUS SYSTEM. 



movements of this kind, though less perfect, are performed 

 by man during sleep, when the cerebral organs are passive, 

 and when the fact of tickling the sole of the foot is followed 

 by a sudden withdrawal of the corresponding leg, or of both 

 legs, etc. From this it maybe remarked that "the greatest 

 number of reflex actions in co-ordination partake of the nature 

 of defensive movements. 



Variations in intensity of the Reflex Actions. Whatever 

 may be the phenomena which take place in the centres of 

 the gray matter (nerve globules) at the time of the produc- 

 tion of a reflex action, it is distinguished by the name of 

 reflex power, or the property possessed by the gray axis of 

 the spinal cord (or similar centres) of transforming centripe- 

 tal impressions into centrifugal reactions ; this expression 

 seems to present a certain convenience of language, for it 

 relates to agents that appear to convey their action upon the 

 reflex power, either to diminish or increase this, without in 

 any way acting upon the centripetal or centrifugal portion 

 of the act, but solely upon the central act. We can here call 

 to mind numerous investigations, by means of which the 

 central action of these agents can in this way be precisely 

 fixed, and we can distinguish among them analogous agents 

 which convey their action upon the peripheral paths; a rec- 

 ollection of the beautiful experiments of Claude Bernard with 

 woorara (curare) on the motor nerves (vide physiology of the 

 muscles, muscular irritability). In connection with the 

 agents that modify reflex power we will cite as examples : 



The surrounding temperature : reflex actions are more 

 energetic and easier to provoke in summer than in winter 

 (Brown- Sequard, Cayrade), but yet reflex power is rapidly 

 exhausted during warm weather ; sections of the spinal cord 

 or its separation from the encephalon: in these cases the 

 reflex actions are exaggerated, which seems to be due to an 

 irritation of the centres even from the act of the section, 

 rather than to the interruption of all communication between 

 these centres and other centres called moderators (Setsche- 

 now) ; and indeed this exaggeration of the reflex power after 

 sections lasts but a short time ; a certain number of poisons 

 convey their action directly upon the centres and exaggerate 

 the reflex power ; among these are strychnine, morphine, 

 picrotoxine, nicotine, veratrine, cicutine, and certain patho- 

 logical products of the organism, as in the septic infections 

 (septicemia), uremia, severe icterus. 



On the other hand, reflex power is diminished by anemia, 



