“ Nuclear Osmosis .” 
H 3 
traction is based upon this volume relations, it is worth while to 
check it. An examination of his own figures shews, however, that 
the space occupied by the nucleus is only about one quarter of the 
of the volume instead of the half assumed by the author. 
But apart from this circumstance, Dr. Lawson’s whole hypo¬ 
thesis bristles with difficulties with which he has not himself dealt. 
For if the contraction of the nuclear vacuole can bring such 
structures as spindle fibres into existence, why cannot the same 
effect he produced by ordinary plasmolysis of the cell ? This 
operation can be very rapidly carried out, but no appearance sug¬ 
gesting spindle formation ever results. Again, why is the spindle 
polarised at all on the assumption of a central contracting vacuole 
as the determining factor of its existence ? How can such a vacuole 
be held responsible for such a structure as may be observed during 
the mitosis of a germinating spore of Pellia for example, or for the 
equally diagrammatic figures of many animal cells ? It would seem 
to be impossible, without piling up an overwhelming load of accessory 
hypotheses to bring all these examples into line by attributing to 
all and every one of them a common origin in forces supposed to 
be exerted by a centrally contracting nuclear vacuole. 
Furthermore, a closer scrutiny of the manner in which each 
chromosome is believed by Dr. Lawson to become severally enveloped 
by a portion of the nuclear membrane, carrying with it a share of 
the adhering cytoplasmic fibrils, seems to reveal still fresh difficulties. 
The vacuole membrane is clearly elastic, the actual contour being 
largely determined by conditions affecting surface tension. The size 
of the vacuole itself is of course mainly dependant on the relative 
concentration, within and without it,of osmotically active substances. 
Now if it be assumed that the contraction is due to permeability of 
the wall, surface tension alone must be responsible for its final 
contraction, and it seems impossible to regard each chromosome 
enveloped separately in its share of the original film as an “osmotic” 
system ” at all. 
Furthermore it is difficult to imagine that a membrane possess¬ 
ing the properties thus attributed to it, of sliding over and enveloping 
the separate individual chromosomes can possible adhere in the way 
postulated, to the achromatic cytoplasmic reticulum in the first 
place assumed to exist, and in the second to be drawn out into the 
fibrillar structures with which everyone is acquainted. If on the 
other hand it is assumed that a sort of plasmolysis is responsible for 
the contraction of the nucleus and the subsequent events, one is 
