264 The Microscope. 



is owing to the fact that observers took no account of the optic 

 illusion produced by the microscope. It is a well-known fact 

 in microscopy, that the lens will only show an optic section of 

 the object; but by a comparison I hope to make this matter 

 clearer. 



Suppose a thread of yarn is wound up into a loose l)all ; by 

 making actual sections with a sharp knife the thread would 

 necessarily be cut into small pieces or coils ; the same thing 

 apparently takes place with the nuclein filament when optic 

 sections are made by means of the microscope. 



I have often directly observed the continuity of the filament 

 by focussing rapidly up or down, so that the image of the pre- 

 vious optic section had not time to De effaced from tlie retina. 

 The same result I have often obtained by focussing slowly up or 

 down, at the same time following with the e3^e ; the thread 

 appearing without any interruption, it is therefore continuous. 

 Sometimes the appearance of the nuclein in the form of short 

 coils is due to some particular cause. In fact cells from the tes- 

 ticles of the grasshopper, the Libellula and Isopoda have nuclei 

 in which the nuclein seems to be in the form of short pieces ; 

 but this again is so in appearance only, for if the cell be stained 

 first by borax carmine and afterwards by methyl green, that 

 philosopher's stone of nuclein, it may be seen that the nuclein 

 tubule is here and there empty, and consequently the staining 

 with methyl green reveals only the spaces which are filled with 

 nuclein ; but the carmine shows that the tubule is continuous. 



The diameter of the nuclein tubule varies also, being generally 

 greater in cells derived from glands and smaller in those taken 

 from the testicles. Sometimes the diameter is uniform through- 

 out the whole length, whilst often the tubule becomes enlarged 

 here and there, so as to assume a moniliform appearance. We 

 have already seen that the nuclein element of the nucleus is com 

 posed of a tubule in which is contained a more fluid substance 

 the nuclein proper ; it is this nuclein which is especially stained- 

 with methyl green, so that this agent becomes the real touch 

 stone of nuclein. This tubule never completely disappears; it 

 persists although broken up, during the various karyokinetic 

 movements which it undergoes during cell division. The nu. 

 clein exisls in the tubule in various forms, sometimes filling it 

 completely, at others forming a layer in the interior against the 



