140 MR A. ANSTRUTHER LAWSON ON 
down and collapse under such circumstances. Nevertheless, the actual breaking down 
has been described and figured by several close and accurate observers. Without 
attempting to question the accuracy of these records, I should like to point out a fact 
which will become more obvious later in this paper. It is, namely, that at the time 
when the membrane is reported to break down, the nuclear cavity has diminished con- 
siderably in size—that there is less karyolymph than formerly. A rational explanation 
for this change is a variation in the osmotic relations—that a part of the karyolymph 
has diffused into the cytoplasm by exosmosis. Under such circumstances it is not 
difficult to understand the collapse of the nuclear membrane upon the sudden 
application of fixing reagents. After a careful re-examination of my own preparations, 
I have not only been convinced that this is really the cause of the breaking down of 
the nuclear membrane, but also that in the normal living cell the membrane does not 
break down. What would happen if such a breaking down were possible in the living 
cell? Clearly the surrounding cytoplasm would be at once exposed to the large 
remaining body of karyolymph, which is a watery fluid. By the very reason of that 
exposure and contact one would expect a new membrane to be precipitated immediately. 
The new membrane would be precipitated so simultaneously with the break that the 
latter could not be detected. For does not the nuclear membrane exist as a membrane 
by virtue of its contact with the karyolymph ? (PrEerrer, 1890; Lawson, 1903; GarTgs, 
1907, YaMANoucHI, 1906). The killing of the cytoplasm by the application of fixing 
reagents would prevent the precipitation of a new membrane, so that any rupture caused 
by such reagents would show in fixed material. 
The growing or pushing in of the fibrils from the base of the cones into the nuclear 
area when the nuclear membrane is supposed to have vanished has also offered some 
difficulties. It is generally admitted that these fibrils are nothing but modified 
cytoplasm, and as such they are viscous and semi-fluid. It seems improbable that such 
fine, delicate cytoplasmic threads should traverse the clear remaining body of nuclear 
fluid—threads which at one moment are reported to be elongating towards the periphery 
of the cell, and in the next, upon the disappearance of the nuclear membrane, are observed 
to traverse or elongate in the opposite direction. Surely something more than the 
vague mystery of “electrical conditions” is needed to account for such extraordinary 
changes. But, as Professor Farmer admits, “the time has not yet arrived when it will 
be possible to give an explanation of these cellular changes that will prove satisfactory 
from a physical point of view.” 
These threads seem not only endowed with the power of traversing the clear watery 
fluid of the nuclear area, but it is reported that they become attached to the chromo- 
somes by their free ends. Now it is a fact that all of the chromosomes become attached 
to fibrils—none of them escape. It seems also that the distribution of the fibrils is 
fairly uniform among the chromosomes. ‘That is to say, the number of fibrils that 
become attached to the various chromosomes is approximately the same, there being 
no striking difference in the size of the fibril sheaves attach to each chromosome as 
