The Morphology and Physiology of the Nucleolus. 123 
summary of the various theories as to its function will serve to 
show that we are still far from having reached any satisfactory 
conclusion as to its real significance in the cell ; and that it 
remains to-day one of the cell organs of whose role in vital 
activities we have the least definite knowledge. 
The various theories that have been advanced may be classified 
in groups as follows : — 
(i.) Waste Product Theories . — Watase (62) held the view that 
the nucleolus merely represented the accumulated waste products 
of the rfucleus, and this view has been maintained by many other 
workers. Wace Carlier considered that it was necessary for such 
waste material to be cast out of the nucleus into the cytoplasm, 
where it might serve some useful purpose. Haecker considered the 
nucleolus to be a pulsating excretory organ with contractile 
vacuoles for expulsion of effete material. 
(ii.) Nutrition Theories. — Derschau (J/.8) looks upon the 
nucleolus as the centre of the vital activities of the cell, and 
fragments of the nucleolus, he says, carry chromatin out to those 
regions of the cytoplasm where it is required for formative 
processes. This is the most extreme expression of this group of 
theories. 
Korschelt held that the nucleolus represented a nuclear 
secretion discharged into the cytoplasm during cell division. 
Montgomery (Jf2) considered that it had an extranuclear origin, 
and that “ it stands in intimate connexion with the phenomena of 
nutrition of the nucleus.’" Sharp (48) holds a similar view as to its 
relation to nuclear metabolism. 
Julin (30) also thought that the nucleolus conducted the 
vegetal processes of the cell ; and Walker and Tozer (59) expressed 
similar views, regarding the nucleolus as bearing, in the form of 
migratory particles, excretory and secretory substances from the 
nucleus into the cytoplasm. 
Nakahara (46) in a recent paper has reconciled the two opposing 
views as to the intra and extra nuclear origin of the nucleolus. 
He writes, “ Different views concerning the nucleoli, and especially 
the question of their origin, can be brought into harmony under 
the hypothesis that the nucleoli represent substances going through 
the nucleus in metabolism. According to this hypothesis, nucleoli 
may be formed directly of a material taken up by the nucleus, or 
may be produced from some substances within the nucleus in the 
course of metabolic processes.” 
(iii.) Binuclear Theories . — The theory that the nucleus contains 
two kinds of chromatin has been put forward by Schaudinn, but 
most ardently advocated by Goldschmidt, who wrote, <c Every 
animal cell is by nature binucleate ; it contains a somatic and 
propagatory nucleus. The former (kinoplasm) presides over 
somatic functions, metabolism and movement. The propagatory 
