576 REPORT—1905. 
see spindle, and these gradually approach until the spindle is approximately 
ipolar. 
The differentiation of the spindle figure appears to be entirely for the pur- 
pose of bringing about the separation of the split halves of the chromosomes. As 
to the exact mode in which the spindle is formed, or the forces which bring it 
about, and the nature of the spindle itself, these are problems which as yet remain 
unanswered. 
Experiments on the Production of Artificial Asters. 
There are two main views as to the nature of the spindle and astral fibres : 
(1) that they represent a definite morphological differentiation of the cytoplasm 
which possesses in itself the power of forming these fibres; (2) that they are 
formed out of the cytoplasm by some modification of its structure or arrangement 
of its parts, or by the precipitation or condensation of some of its constituents. 
The aggregation of granules into radiating fibrils can be imitated artificially by 
allowing a drop of alcohol or turpentine to fall upon smoked glass. If the drop is 
allowed to fall from a good height, we get the artificial centrosomes with radiations 
first described by Henking; these are due mainly to the splash of the drop and 
its breaking-up into small particles which radiate outwards, carrying portions of 
the smoke film with them. If the drop is allowed to fall more gently, so that it 
does not splash, its first effect is to produce a clearly circumscribed circular ring, 
and then, by slowly spreading outwards, to produce an aggregation of the smoke 
particles into fibrils which more nearly represent the appearances produced in 
cytoplasm than do Henking’s splashes. 
By careful manipulation we can get in this way representations of the centro- 
some or centrosphere, or even the radiations around the nucleus. If the edge of 
the alcohol or turpentine be carefully examined under the microscope as it is 
slowly spreading outwards, a violent motion of the smoke particles will be 
observed as soon as the liquid comes into contact with them, and as the liquid 
passes on these particles settle down into definite continuous fibrils, which go on 
growing as the liquid continues to spread. Although I do not wish to push the 
analogy too far, it seems to me that in the same way the excretion of a liquid from 
the nucleus or centrosome into the cytoplasm may set up surface-tension pheno- 
mena of a complex character which wouid lead to the aggregation of the granular 
cytoplasm into radiating fibrille, or to the precipitation or coagulation of the 
proteid substances with a subsequent fibrillar aggregation. In any case the 
possibility that it is due to some physico-chemical changes brought about by the 
active metabolism of the nucleus or cytoplasm is not excluded, and it is much to 
be desired that this field of experimental investigation should be more fully 
explored. 
Fischer has described the formation of artificial asters by two methods: (1) If 
pith is injected with proteid and then fixed, asters are found around small 
particles of foreign matter in the proteid. (2) If a small granule of corrosive 
sublimate or a drop of osmic acid be brought into a proteid solution radiating 
strize are formed in it by precipitation. He suggests that the centrosome is formed 
by the precipitation of albuminous substances in living cells by the excretion 
of nucleic acid from the nucleus, and that, as in (1), artificial radiations are 
formed around it by the action of the fixing reagents; or possibly by the fixative 
action of the nucleic acid itself. Or the centrosome itself may produce them, as 
in (2), by acting as the precipitating agent, just as corrosive sublimate or osmic acid. 
Mr. Jenkinson has recently described some interesting experiments on the artificial 
production of asters, and comes to the conclusion that osmotic pressure and 
surface tension are probably concerned in the formation of these structures in the 
living cell. The centrosome may be a body capable of withdrawing water from 
the cytoplasm, of swelling up and dissolving in the water so absorbed, and then 
giving off radial outgrowths which precipitate the proteids of the cell, and so form 
astral rays; or the centrosome may undergo decomposition, or may secrete a 
ferment which would have the same effect upon the cytoplasm, 
