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it is a theory that will work, it is not a theory one can work with.” It has been 
shown, conclusively the authors think, that heritable variability is synony¬ 
mous with genotypic impurity. In those cases where we are sure that the origin 
of the group ensures purity of the genotype selection has been shown to be 
ineffectual (Johannsen’s law). Thus we do not need to make provision, in our 
theory of the nature of genes, for qualitative variability in the genes themselves. 
And this point, in their view, is the only j ustification for the supposition that 
the genes are protoplasmic. “ Protoplasm is clearly an emulsion, and it must be 
ultimately made up of a number of non-living substances, the combination of 
which makes it living.” The attitude of the vitalist who reasons that every 
constituent of protoplasm which is an integral part of it and which shows one 
or more of the properties of protoplasm is itself protoplasmic may be compared 
to the attitude “ of a philosophically minded eater of plum-pudding, who should 
argue that the round sweet things he could dissect out of his helping, and 
which looked like raisins, could not be raisins; since he found them in his 
plum-pudding and forming an integral part of it they must consist of plum¬ 
pudding.” 
Quantitative propagation combined with qualitative stability is not ex¬ 
clusively a property of protoplasmic bodies multiplying by bipartition. Auto- 
catalytic chemical substances fulfil both requirements, since they propagate 
themselves, i.e. suitable materials are changed into a new substance under 
the influence of that substance. Also they remain qualitatively unchanged 1 . 
The theory that genes are of this nature is believed by the authors to be com¬ 
patible with all the facts known about the action of genes. 
All the circumstantial evidence certainly points to the conclusion that the 
chromosomes are ultimately bound up with the process which leads to a dis¬ 
tribution of the genes over cell generations, and there is no incompatibility 
between the view that the genes are of a relatively simple chemical nature, 
and that they are in some way localised in or on the chromosomes. 
We may perhaps suppose that a complete set of genes is kept intact inside 
the nucleus, and we must probably take the view that there is no real difference 
between the nuclei of “germ” cells and those of “somatic” cells. The facts 
of regeneration of the whole plant from single somatic cells are fairly decisive 
for this view. But the cytoplasm of individual somatic cells of different tissues 
certainly has strikingly different chemical, physiological and morphological 
properties, and this may be due to the quantitative preponderance of one or 
two genes (autocatalysts) in extremely differentiated cells. 
We cannot directly compare a multicellular with a unicellular organism. 
The cells of the former that are in immediate contact with the environment 
have, as a rule, no “future,” i.e. they have no germ cells among their descen¬ 
dants. If we conceive of a gene as simply a chemical substance, the taking up 
of a new gene by a unicellular organism may not be an impossible or a rare 
process. But it is significant that, according to our authors, no authentic case 
of a positive mutation in the higher plants or animals is on record. And we must 
beware of accepting instances of the effect of selection in apparently pure clones 
of unicellular organisms as invalidating Johannsen’s law. 
1 See A. I.. Hagedoorn, Vortrage und Aufsdtze uber Entwicklungsmechanik Roux. 
Leipzig, 1911. 
