142 
J. Bretland Farmer. 
they act, and finally that, with our growing knowledge of the 
physics of colloids, many reactions and dissociations which would 
have appeared impossible a few years ago, are now recognised as 
not only possible, but are actually known to occur at the same time. 
The writer, still holds that “ the time has not yet arrived when it 
will be possible to give an explantation of these cellular changes 
that will prove completely 1 satisfactory from a physical point of 
view.” 
Obviously this must continue to be true until we know a great 
deal more about the nature of protoplasm and the dissociations 
and other changes that go on within its substance. But it seems 
absurd to compare, as Dr. Lawson does, a working hypothesis, 
however incomplete, but based on electrical conditions of which 
we do know something, with mystical notions on “ cell polarity ” 
of which, as an efficient cause, we know absolutely nothing. 
Dr. Lawson’s own working hypothesis seems to be somewhat 
as follows. The nuclear cavity really represents a vacuole filled 
with sap as well as with other solid matter, chromatin and the like 
The vacuole is contained in a semi-permeable membrane (the 
author continually calls it a permeable membrane, but this is per¬ 
haps a slip, as, of course, semi-permeability is of the essence of an 
osmotic system). The extra nuclear protoplasmic “ reticulum ” is 
continuous, with the nuclear wall, which itself is supposed to be of 
cytoplasmic origin. Contraction of the nuclear cavity (vacuole) at 
and after diakinesis produces a strain in the continuous cyto¬ 
plasmic reticulum (which seems to be assumed to represent a 
permanent structural differentiation), and this contraction is thus 
held to be responsible for the first appearance of the spindle fibres. As 
the vacuole continues to contract, the fibres become more and more 
pronounced owing to the tension supposed to be thereby developed 
in the reticulum, and finally each chromosome becomes separately 
enveloped in the infolding vacuole wall. In this way, it is 
believed, each of these bodies comes to possess its own sheath of 
fibres. The result is that, instead of a single osmotic system repre¬ 
sented in the nucleus, we now have established as many indepen¬ 
dent “osmotic systems” as there are chromosomes. 
Dr. Lawson considers that the nucleus before its period of 
contraction occupies a cubic capacity of about half that of the cell, 
and since part of his argument as to the striking effect of the con- 
1 Dr. Lawson, doubtless by inadvertence, omitted the word 
“completely” when quoting the above passage, thereby 
altering the sense of the original in no small degree.” 
