566 Humphrey. — On some 
believed they have observed such a change. It is a common 
observation that a disappearing nucleolus within the nucleus 
often loses its staining power more rapidly than it decreases 
in size, though remaining distinctly stainable to the last. 
These facts seem to confirm the belief that the nucleoli are 
indefinite masses of a reserve substance, which, for want of 
chemical knowledge, we must call nucleolar substance, or, 
with Schwarz, pyrenin , and which undergoes a chemical 
change, in consequence whereof it loses its power to take up 
stains. They are, then, strictly comparable, to borrow my 
previous comparison, with the drops of oil in the Castor Bean, 
which disappear as oil-drops during the active life of the 
plant, to reappear in the resting-stage of the new seeds. 
There is no evidence that the nucleolar substance which 
appears in the daughter-nuclei after division is identically the 
same as that which disappeared just before the division. It 
can only be said to be a chemically similar substance. The 
fact that not all of the nucleolar material in a cell is always 
changed, may show nothing more than that more may some- 
times be produced than can be changed at once. We know, 
as yet, so little about the part played by this substance and 
about the relation of nutrition and other conditions to its 
formation in the cell, that it is idle to speculate upon its 
significance. 
The latest view of the role of the nucleoli 1 is that of 
Strasburger (’95), who is led by his observations on Larix to 
believe that they furnish the material for the formation of the 
spindle-fibres. I can add nothing at present to the discussion 
of this question. 
Zimmermann’s demonstration of the not infrequent passage 
of nucleolar substance into the cytoplasm, and the pretty 
generally accepted fact that in many cases extranuclear sub- 
stance contributes to the spindle-fibres, deserve emphasis as 
indicating a free interchange between all parts of the cell, 
1 More exact information concerning the nature of the nucleoli in animal cells, 
and whether any of the bodies included by zoologists under this name are 
chemically similar to the nucleoli of plants, is greatly to be desired. 
