TRANSACTIONS OF SECTION K. 571 
activity is seen in the increased staining capacity of the chromatin thread and in 
the changes which take place in the nucleolus, by which it becomes very irregular 
in shape and closely connected by threads to the chromatin network. In many 
cases the nucleolar substance appears as if being drawn out into the threadwork, 
and the nucleolus appears as if some active change were taking place in it. 
It is very difficult to escape the conclusion that we are here dealing with a 
series of changes in the chromatin thread which are intimately bound up with the 
activity of the nucleolus, and it is probable that the imereased stainability of the 
chromatin is due to an actual transference of a portion of the nucleolar substance 
into the thread. 
We know very little of the causes which bring about the rearrangement of the 
nuclear substances which lead to the formation of the chromosomes. The regu- 
larity of the sequence of events in the process seems to me to preclude the 
possibility that they are due merely to changes set up by the action of reagents. 
It is very probable that the metabolic activity of chromatin itself, and possibly of 
that part of it which is stored up in the nucleolus, plays a significant part in 
these phenomena. Sinapsis, for example, may be set up by diffusion currents 
between the nucleus and the surrounding cytoplasm, brought about possibly by 
the secretion of nucleolar or chromatin substance, or to interactions taking place 
between it and the cytoplasm. 
Experimental Observations on the Activities of the Nucleus. 
So far as I know no experimental investigations into the causes which bring 
about the changes in the prophases of nuclear division have been made, but it is 
not difficult to imitate artificially some of the phenomena observed. Olive oil is 
shaken up in amixture of methylated spirit and water of such a strength as will 
allow the oil globules to float. A shallow petrie dish, three or four inches in 
diameter, is then taken ; the mixture of oil and dilute methylated spirit is well shaken 
until the oil is broken up into very fine globules, and the mixture is at once poured 
gently into it. The appearance of the mixture is that of a homogeneous mass of 
small oil-globules distributed through the solution, and can be compared to the 
granular appearance of a nucleus in a resting stage. The spirit at once begins to 
evaporate, and currents are at once set up in the solution in such a way that the 
globules of oil gradually become restricted to certain areas only, and a coarse granular 
network is formed somewhat like the early stages in the aggregation of the chromatin 
granules into a spireme in the nucleus. The network gradually becomes more and 
more clearly defined, and then, just as is the case in the nuclear network, it begins 
to show a double row of granules, which finally becomes very clear and distinct. 
The threads become shorter and thicker and break up into irregular lengths, 
which gradually mass themselves together into an irregular heap or heaps of 
fusing oil-globules either in the middle or at the periphery of the petrie dish. 
We have, in fact, a good imitation of the earlier stages in the prophases of division 
of the nucleus, and it seems not unlikely that the aggregation of oil globules in 
our petrie dish may afford some clue as to the possible means by which the 
aggregation is brought about in the nucleus. 
Ido not suggest that the complex phenomena which take place in nuclear 
division are to be explained as due simply to such phenomena as diffusion, surface 
tension, and the like, or any other physico-chemical processes. We must be very 
careful not to attempt to force merely physico-chemical explanations upon such 
phenomena as these. Without admitting the necessity of anything akin to 
a special vital force, we are compelled to admit that vital phenomena do not 
at present admit of a merely mechanical explanation. But it does seem to me 
possible that the metabolic activity of the nuclear material at this stage 
may be accompanied by phenomena referable in part to these agencies. If, for 
example, active metabolic activities are set up between the nucleus and cytoplasm 
_through the nuclear membrane, as seems probable, it is quite conceivable that this 
would bring about diffusion currents which might be taken advantage of in pro- 
ducing the aggregation of the more solid parts of the nuclear substance into a more 
