28 
THE ORGANIC CELL 
the fibrillar and alveolar. The most recent work tends to show 
that neither of these theories has succeeded in giving a universal 
type for the structure of protoplasm, and probably Kolliker’s 
early opinion is correct : viz. that the different appearances 
described in each theory are connected by intermediate stages 
and may be transformed one into another during cell activity. 
According to Flemming, no single type can be characterised 
as diagnostic of the living substance. It is probable that the 
protoplasm of the same cell may at one time be homogeneous, 
at another fibrillar, and at another alveolar, according to its 
period of growth, &c. The source of physiological activity 
in living protoplasm must probably be sought for in its ultra- 
microscopical organisation. 
The Nucleus 
A portion of a cell from which the nucleus has been removed 
will live for a considerable period of time and will show response 
to stimuli. This enucleated mass of protoplasm, however, 
cannot repair its lost portions, neither can it grow, and more 
important than all, it is unable to assimilate to itself those 
substances by which a prolonged existence can be maintained, 
and by which energy can be stored up. After a somewhat 
brief existence its fate is but to die. To state the case in 
another way, it may be said that the enucleated mass of 
protoplasm possesses the functions which require destructive 
metabolism, and the functions persist probably until the reserve 
of potential energy has been resolved into kinetic energy. 
From many experiments it has been clearly shown that the 
nucleus is the chief factor in the constructive or synthetic 
metabolism of the cell. 
That the nucleus possesses this most important function of 
synthetic metabolism is demonstrated by the fact that digestion 
of food and growth cease with its removal. It is also indicated 
‘ by the position and movements of the nucleus in relation to 
the food-supply and to the formation of specific cytoplasmic 
products.’ It also agrees with what is now universally ad- 
mitted, that exchanges of material occur between nucleus 
and cytoplasm. The varying changes of staining capacity 
exhibited by the chromatin of the nucleus during the life of 
