52 
Walter Stiles 
Hopkins (1913) thinks the biogen molecule theory “as inhibitory 
to productive thought as it is lacking in basis.” Bayliss (1915) 
regards the biogen theory as “ an example of the efforts of a certain 
school of physiologists to explain by purely chemical laws, such 
as mass action, facts which admit of a simpler explanation, if 
physical phenomena are also taken into account.” 
We have to think of protoplasm not merely as an intimate 
mixture of a large number of substances, but as having a complex 
organisation so that the cell is rather an organ with an intricate 
minute structure, and at the same time different reactions can 
take place in different parts of the same cell. “Protoplasm is an 
extraordinarily complex heterogeneous system of numerous phases 
and components, continually changing their relations under the 
influence of electrolytes and other agents” (Bayliss, 1919). For a 
further discussion of this question reference may be made to the 
writings of Verworn, Czapek, Hopkins and Bayliss cited above. 
Some parts of the protoplasm are clearly differentiated from the 
rest. The most important of these is the nucleus which has been 
observed in all plant and animal cells with very few exceptions. 
From its appearance in fresh cells and from its reaction to stains 
it obviously differs from the cytoplasm that encloses it. There is 
considerable evidence that it is much richer in nucleoproteins, 
which contain phosphorus, than the surrounding cytoplasm. The 
observations of Gaidukov and Price with dark-ground illumination 
point to the fact that the nucleus is in the gel condition. Kite (1916) 
and Chambers (1917) conclude on the contrary that the resting 
nucleus of the ovum is in the sol state. Price made out a definite 
limiting layer separating the nucleus from the cytoplasm, but he 
thinks it possible that this, the so-called nuclear membrane, may 
be no more than the surface of separation between the cytoplasmic 
hydrosol and the nuclear hydrogel. The intimate connection be¬ 
tween cytoplasm and nucleus as regards cell activity is so well 
realised that it needs no further emphasis. 
The plastids occur only in plants, and even then not in all 
plants. They are absent, for example, from the Fungi. Like the 
nucleus they are sharply differentiated from the rest of the cyto¬ 
plasm and appear to contain much protein. In addition they often 
contain pigments (chlorophyll, xanthophyll and carotin) our know¬ 
ledge of the composition of which is due to the persistent researches 
of Willstatter (1913). According to Price the chloroplasts of Spiro- 
gyra, Elodea and other plants are, like the nucleus, in the gel state. 
