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SCIENCE 



[N. S. Vol. XLVII. No. 1207 



no change of any kind whatsoever can be 

 discovered in the dorsal root, showing that 

 the same path can not be traversed in the 

 reverse direction. As intraneural conduc- 

 tion is well known to occur in both direc- 

 tions this interruption is believed to be 

 interneural, that is, synaptic; hence the 

 conclusion that the synapse is a valve-like 

 mechanism that permits the passage of an 

 impulse in one direction only. The polar- 

 ity of a deep-seated neurone then is deter- 

 mined by its synapse. 



If we divest our minds of the assumed 

 nervous significance of the cell body of the 

 neurone and of all the misleading termi- 

 nology of cellulipetal and cellulifugal con- 

 duction in relation to dendrites and neu- 

 rites, we have left the simple proposition 

 that neurones, though capable of double 

 conduction within themselves, nevertheless 

 conduct normally in one direction only. 

 This is the real and sufficient basis for neu- 

 ronic polarity. That it is partly dependent 

 upon the synapse is quite obvious. For 

 this and other reasons the synapse has been 

 a matter of much concern to neurologists, 

 but its extreme minuteness has been a 

 baffiing feature in its investigation. The 

 researches of His (1886) supported by 

 those of Harrison (1901) and others have 

 shown that in many parts of the nervous 

 system neuroblasts that give rise to con- 

 tiguous neurones in adult neuronic chains 

 may be in embryonic stages far separated 

 and come together only after considerable 

 growth. Of their initial separation there 

 can be not the least doubt; the question 

 that naturally arises concerns the extent of 

 their final union as they establish synaptic 

 relations. That this can not be complete 

 has already been pointed out in discussing 

 synaptic transmission, but precisely what 

 the incompleteness consists in from a his- 

 tological point of view is by no means easily 

 determined. Bartelmez (1915) has had 



the opportunity of studying the synapse 

 under conditions in which the elements 

 were extremely coarse (the Mauthner's 

 cells of fishes) and he finds, as might have 

 been expected, no continuity, but delicate 

 membranous separations. These mem- 

 branes must be the parts concerned with 

 synaptic activities and hence with the 

 polarity of the neurone so far as it is de- 

 pendent upon the synapse. 



Thus after years of infinite pain and 

 labor the neurologist of to-day can describe 

 in terms of cells the nervous system of one 

 of the higher animals as composed of an 

 intricate association of neurones whose re- 

 lations to the animal as a whole and to each 

 other through synaptic contact have im- 

 pressed upon these structures a definite 

 form of polarity. 



As this idea of the synaptic nervous 

 system gradually unfolded itself to the 

 more orthodox neurologists, there arose 

 from another school of workers the dia- 

 metrically opposite conception of the nerve- 

 net. This new movement received its ini- 

 tial impetus chiefly from the work of 

 Apathy (1897), who maintained on the 

 basis of preparations of almost incredible 

 clearness that the nervous elements of 

 many animals were bound together by a 

 network of neurofibrils in which there was 

 not the slightest evidence of interruption 

 such as is implied in the synapse. This 

 view in a way was a revival of the idea of a 

 continuous network as maintained in a 

 previous generation by Gerlach. The 

 careful reader of Apathy's papers will find 

 it by no means easy to separate in them 

 fact from speculation and consequently it 

 is difficult to state in exact terms Apathy's 

 real contribution to this subject, but, how- 

 ever this may be, it is certainly true that 

 the appearance of his publications excited 

 others to a further investigation of the 

 subject with the result that nerve-nets were 



