240 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
To grant that the network which is described as surrounding the 
sense cells is nervous in character would not necessitate the abandon- 
ment of the neurone theory, though such a structure would of course 
be in perfect accord with Apéthy’s conception. Kolmer admits, 
however, that his conclusions are based upon rare observations, 
and he assumes that in the great number of cells which do not show 
pericellular networks of neurofibrillae their non-appearance is due to 
imperfect impregnation. He also assumes that his inability to find 
evidence of such structures in fishes is due to ‘‘some specific physico- 
chemical characteristic of fish protoplasm which renders these verte- 
brates unfavorable objects for the study of peripheral neurofibrillae.” 
I know of no evidence for the truth of such an assumption. I have 
already pointed out good reasons why we should expect fishes to 
furnish the best material in the vertebrate series for the study of this 
problem. 
Bielschowsky und Briihl, like Kolmer, base their belief in the 
existence of pericellular networks upon rare observations, assuming 
that the more numerous and more simple structures are the result 
of imperfect impregnation, and that the rarer pericellular networks 
represent a universal terminal structure. ‘his appears to me to be a 
dangerous assumption, and I believe that the safer course would be to 
look with suspicion upon structures of such rare occurrence, regarding 
them as probably artefacts. It would perhaps appear presumptuous 
for me to venture a criticism upon the handling of a method which 
Bielschowsky himself worked out. Nevertheless, it should be recog- 
nized that, superior as this method is to the older impregnation proc- 
esses, it is easy, by overdoing the treatment with the silver oxide 
solution, to cause almost any tissue to take on the color characteristic 
of nervous matter in good Bielschowsky preparations. I have several 
times obtained preparations in which the sense hairs, and the sense cells 
as well, were entirely blackened, and have seen preparations from the 
lateral line region in which muscle fibres were well impregnated, the 
cross striations being clearly differentiated. I have no doubt that by 
excessive treatment with silver oxide solution it would be entirely 
possible to cause non-nervous intercellular material to take on the 
appearance of nervous substance. What constitutes successful im- 
pregnation is a matter which it is necessary for each investigator to 
determine for himself, and it is this last resort to the personal judgment 
of the investigator which is responsible for many of the differences 
of opinion in this field. The controversy between the neuronists and 
the fibrillists has resolved itself largely into the question whether certain 
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