THE BUILDING OF REFLEX ARCS 245 



in 1911, as well as the recent work of Professor Woods Jones on 

 Arboreal Man, are full. Indeed if the construction of new reflexes 

 and reflex -arcs in organic evolution " forged by an incident of use " 

 as Professor Macdonald puts it, were expunged from these works, 

 their treatment of the physiology of the central nervous system 

 of higher animals would be emasculated, to say the least of it. And 

 yet not one of these eminent men is writing ad hoc, or for the con- 

 fusion of Weismann and his followers. At this point it may perhaps 

 gain for the remaining pages a little more consideration from 

 opponents if I give a few quotations from these writers in support 

 of the foregoing statement — perhaps the breeze of authority may 

 then carry my little bark a little further on its perilous voyage. 

 Professor Sherrington remarks on the first page of his well known 

 work, in reference to the cell -theory, " with the progress of natural 

 knowledge, biology has passed beyond the confines of the study 

 of merely visible form, and is turning more and more to the subtle 

 and deeper sciences that are branches of energetics. The cell- 

 theory and the doctrine of evolution find their scope more and more, 

 therefore, in the problems of function, and have become more and 

 more identified with the aim and incorporated among the methods 

 of physiology." Again, " Mere experience can. apart from reason 

 mould nervous reactions in so far as they are plastic. The * bahnung ' 

 (or facilitation) of a reflex exhibits this in germ." He uses more 

 than once the pregnant phrase, " The canalizing force of habit " ; 

 again, ' ; Progiess of knowledge in regard to the nervous system has 

 been indissolubly linked with the determination of function in it." 

 Speaking of the receptive-field he says of the central nervous system, 

 " To analyse its action we turn to the receptor organs, for to them 

 is traceable the initiation of the reactions of the centres " ; of the 

 extero-ceptive field he says, " facing outwards on the general 

 environment it feels and has felt for countless ages the full stream 

 of the varied agencies for ever pouring upon it from the external 

 world," page 20, and " each animal has experience only of those 

 qualities of the environment which as stimuli excite its receptors, 

 it analyses its environment in terms of them exclusively. The 

 integration of the animal associated with these leading segments 

 can be briefly with partial justice expressed by saying that the rest 

 of the animal, so far as its motor machinery goes, is but the servant, 

 of them. Volitional movements can certainly become involutary, 

 and conversely, involuntary movements can sometimes be brought 

 under the subjection of the will. From this subjection it is but a 

 short step to the acquisition of co-ordinations which express them- 

 selves as movements newly acquired by the individual," and, 



