484 MESSRS. F. GOTCH AND V. HORSLEY 



(6.) Summation of Stimuli. A most characteristic feature of the functional activity 

 of a nerve centre is its property of summating (STIRLING) subminimal stimuli with 

 the effect of producing an apparently complete discharge. 



D. The channel of communication between a spinal and other centres may be 

 briefly alluded to as follows : 



(a.) Relation of one spinal nerve centre to another. It is not possible on this point 

 to improve upon the classical "Gesetze" of PFLUGER,* viz., that 



(1.) In a simple reflex the muscular response is always on the same side as the 

 excitation. 



(2.) If a reflex is bilateral, the analogous muscles of the opposite side are thrown 

 into action. 



(3.) If a reflex is bilateral, the movements on the side opposite to that stimulated 

 are much weaker than those on the same side. (Cf. our results on p. 494.) 



(4.) If associated reflex centres are excited, the association is found to have an 

 ascending arrangement in the spinal cord, culminating in the medulla oblongata ; 

 whereas of the encephalic reflexes the association is of a descending character, and also 

 culminating in the bulb. 



(b.) Conduction. SCHIFFJ showed, by section of the crossed pyramidal tract, that 

 the fibres running in it to the lowest spinal centres were undoubtedly the channels of 

 conduction from the encephalon. 



ExNERj came to the conclusion, by time measurements, that there was a delay 

 experienced by the excitatory condition or impulse traversing the spinal centres, 

 when, the descending tracts in the cord having been excited, muscular contractions 

 followed ; but he admits that his results do not permit of a demonstration of the 

 amount of time lost. 



SECTION 2. EXPERIMENTS BY THE GALVANOMETRIC METHOD DIRECTLY BEARING 

 UPON THR STRUCTURE OF NERVE CENTRES. 



(l.) Resistance offered by the Efferent Side of the Centre to the Passage of Impulses. 



The results which have been obtained by our method are best arranged according to 

 the particular part of a nerve centre to which they appear to refer. 



In considering the anatomical structure of a nerve centre as we have given it on 

 p. 479, it is evident that the region of greatest obscurity is that which we have 

 termed the area or field of conjunction between the afferent and efferent sides, and 



* ' Die sensorischen Functionen des Riickenmarks der Wirbelthiere,' v. E. PFLCGEK. Berlin. 1853. 

 f ' PFLUGER, Arcliiv,' vol. 30, 1883, p. 248. 

 J ' PFLUOBR, Archiv,' vol. 8, 1874, p. 537. 



