()0 Buchanan 



rnent of circulation, and variatiorts in the threshold resistances of individual 

 synapses, some of them being forced and not others, or others not until 

 later. 



The late appearance of a crossed-reflex effect, if it appears at all, in the 

 normal preparation, seems to me, on the other hand, to be much more 

 probably due to some factor in the set of secondary synapses preventing its 

 earlier appearance, since, while the same-limb reflex response is com- 

 paratively easy to evoke in the normal cord (it was obtained in about 70 

 per cent, of my cooled preparations), the crossed-reflex response is rarely, if 

 ever, evokable from it by a single instantaneous stimulus to the aflerent 

 nerve fibres, and even in the strychnine cord the crossed-reflex response is 

 so often not to be evoked when that of the same side is showing in its record 

 the eflects of the drug. It is clear that in such case something else has to 

 happen before the extra excitability thus shown to have been brought about 

 in the primary synapses or their cells, can be taken advantage of by the 

 impulses which may come to them from the opposite side of the cord. If 

 these arrive at all at the primary synapses in the normal, or in the lightly 

 strychnised cord, they behave like impulses produced by artificial stimuli 

 too weak to be effectual, applied to the same-side aflerent nerve fibres. It is 

 only when the collective discharge from the cells of the secondary synapses 

 has reached, and passed, its threshold value with regard to the primary 

 synapses and their cells, that it is able to produce an eflfect in the muscle 

 supplied by these. Yet we have seen that strychnine may, when it has 

 acted for a longer time (insufiicient, however, to make the electrical effect 

 serial or the mechanical one a spasm), have a considerable influence on that 

 factor in the secondary synapse which determines the delay in it, and it is 

 most unlikely that what it influences so strongly, it influences less soon 

 than what it influences less strongly, namely, the delay-regulating factor 

 in the primary synapse. Just for this reason, and for the one that other 

 factors also, such as fatigue, seem to have greater influence on secondary 

 than on primary synapse time, I would suggest that it is the individual 

 variability of the time taken in passing the secondary synapses (the 

 variability in their threshold resistances perhaps) in the normal cord which, 

 by preventing the discharges from being synchronous, prevents them from 

 affecting the primary synapse cells and hence the muscle. When, either by 

 making the excitability of the secondary synapse cells more alike, or by 

 making the resistances of the secondary'' synapses more equal, the separate 

 discharges become not only stronger, but more synchronous, they are able to 

 effect what even discharges of the same strength could not do, one by 

 one, with broken step (if one may use the expression). To make effectively 

 to work together things the temporary capacities of which vary, would 

 take a longer time for the drug to accomplish than when it has to 

 deal with things the capacities (Fahigkeiten) of which vary but little, 

 as in the case of the primary synapses. The fact that the first time 

 a crossed-reflex eflect appears after failures to obtain it, in any particular 



