662 Balls.—The Mechanism of Nuclear Division. 
Society very kindly procured me the Zeiss 3 mm., 1-40 num. ap., horn, imm., 
apochromatic objective; the rest of the work was done entirely with this. 
The eyepieces used were Nos. 1 and 4, with the Zeiss compensating 
oculars 1 1 and 18, on a tube of 160 mm.; most of the observations were 
effected with the 12, using the 18 to differentiate in depth. 
Lighting had to be considered very carefully, for the univalent chromo¬ 
somes are little larger than the wave length of sodium light. It was there¬ 
fore necessary to reduce the wave length of the light employed. In this 
respect the use of haemotoxylin had a great advantage, as it stains from black 
to grey. A water tank filled with a strong filtered solution of copper oxide 
in ammonia was placed before the Welsbach incandescent lamp, and its 
concentration was adjusted by the spectroscope until no light passed through 
below the D line. The full aperture of the condenser was used. 
When the Welsbach lamp was in use, an image of the crossing of two 
wires of the mantle was focused upon the object. Later on, critical 
illumination was obtained by using a flat-wicked oil lamp. 
Microphotographs were made of all the important stages. This 
method had its limitations, on account of the roughness of the apparatus, 
but it gave evidence in support of the eye. 
The precise position assumed by the bivalent chromosome at the 
splitting of the spireme, and the number of spindle fibres formed for each 
chromosome, could not be ascertained by the methods I employed. 
Conclusions. 
The nucleus is an independent portion of the cell, morphologically dis¬ 
continuous from the cytoplasm, and consisting solely of chromatin and 
achromatic substances. 
The nuclear sap and membrane belong to the cytoplasm, serving to 
conduct the chemical interchange between nucleus and cytoplasm. 
Assuming that our arbitrary mode of recognition of chromatin and 
achromatin is approximately just, it would seem that their respective 
functions might be somewhat as follows :— 
Chromatin. 
A mixture of complex bodies, probably the bearers of the hereditary 
qualities, incapable of automatic motion, constant in composition for any given 
race, and capable of synthesis only upon a pre-existing basis of their own kind. 
The movement of chromatin along the linin thread from nucleolus 
to chromosome, and conversely, is due to progressive conversion of oxy- 
chromatin into chromatin, granule by granule. The excretion of chromatin 
which seems to take place in some cases might be merely extrusion of 
unnecessary, duplicate ‘ molecules ’. When such extrusion is chemical the 
residue is oxy-chromatin. 
