306 Allen . — The Early Stages of Spindle- Formation 
seems highly probable that it is located within the fibres 
themselves, and that its source is to be sought in chemical 
transformations — destructive metabolism — occurring in the 
substance of the fibre concerned. Since the volume of the 
kinoplasm remains relatively constant during considerable 
periods, constructive metabolism must go on side by side 
with the destructive process ; the kinoplasm, then, in a period 
of activity, is to be thought of as in a condition of more or 
less rapid change ; it is being built up at the expense of some 
of the surrounding non-fibrous substance, perhaps of already 
living cell-constituents, perhaps of non-living but complex 
foods. The energy displayed by a particular fibre represents 
the difference between the energy of formation of the food 
which it receives, and that of the waste products which result 
from the destruction of its substance. It then becomes 
possible to define an active kinoplasmic fibre as the area 
within which certain energy-changes are occurring ; and the 
mass of the fibre is the sum of the masses of the substances 
within that area at the present moment, some of which are 
being built up, some being torn down, while still others may 
remain for a greater or less period unchanged. 
This notion of the nature of kinoplasm seems to be, as far 
as it goes, identical with the suggestion of Wilson (’95), when 
he defines a cell-organ as ‘ a differentiated area of the cell- 
substance in which a specific form of chemical change occurs.’ 
From this point of view, too, it is correct to say that the 
spindle-fibres are expressions of forces at work within the 
cell ; but while admitting the possibility of defining certain 
organs from the point of view of the energy-changes occurring 
in them, I think it is important to insist upon the mass of 
evidence already referred to which points to the existence of 
a distinct fibre-substance. The fibres, that is, are something 
more than paths or lines of force, or mere expressions of 
strains and stresses ; they are organs built up of a substance 
or of substances with distinctive chemical and physical pro- 
perties, which properties determine the power of the organ to 
do particular kinds of work. The organ owes its existence 
