682 TRANSACTIONS OF SECTION K. 
that will arise in conformity with the environment, is irrevocably determined 
long before the organs themselves are sufficiently developed to be exposed to the 
direct influence of the conditions to which they are supposed to be specially 
adapted, 
ae it is a matter of common knowledge that the formative processes can be, 
and sometimes are, disturbed with the most surprising results. I may again refer 
to the fungal or insect galls as examples that will be familiar to everyone. It 
appears to me that these exceptional developments are of extraordinary importance 
in relation to any endeavour to probe the mysteries of organisation. The very 
difficulty experienced in imitating the effect of the iusect’s secretion strongly em- 
phasises the specialised nature of the particular substance which is able to modify 
the ‘normal’ reactions of the plant. The latter are dependent on the way in 
which the organic apparatus determines the fashion of the molecular presen- 
tations, so that, as I have said, the course of the reactions themselves become 
increasingly limited in their range. Now as regards the mauner in which the 
secretion of the insect operates, it seems clear that it can produce no permanent 
change in the organising apparatus of the protoplasm, since the growth is at once 
arrested on the removal or death of the insect. But whether the influence is one 
that more directly affects the physical state of the apparatus for the time being, 
or whether it acts more directly by introducing new substances into the final 
chemical reactions, are questions which are plainly worth investigation, but at 
present certainly do not admit of an answer. 
Another example of interference with the developmental processes is afforded 
by the well-known ‘lithium larva,’ which was discovered by Herbst to arise when 
the eggs of some species of sea-urchins are allowed to segment in sea-water that 
has been altered by the addition of lithium salts. The monstrosity produced 
under these conditions was just as constant and specitic in character as are the 
different galls which can be induced to develop on an oak leaf by the corresponding 
species of insect. 
Extending these considerations a little further, one sees that what we call 
disease also falls into the same category. For disease represents the necessary 
outcome of a disturbance, however introduced, into the course of metabolism, 
which diverts it from the ‘normal’ channels. Pathology has long recognised that 
the explanation and the consequent control of disease lies, ultimately, in the correct 
appreciation of the cellular reactions as the result of their experimental study. 
We cannot pride ourselves on the advances that have been made in the study of 
plant pathology as yet. Our remedies are commonly of the crudest kind, and we 
have only recently begun to take serious count of the facts of organisation in the 
scientific attempt to breed races of plants immune from the attack of certain 
diseases. The results that have already been obtained, both abroad and by Biffen 
and others in this country, are full of hope at the present time. The study of the 
caus+s of immunity along scientific lines ought assuredly to form a fruitful field of 
investigation in the near future. 
From what we already know it seems clear that the proximate causes of 
immunity may be diverse in character, and may consist in very different reactions 
in different cases. It may be that the response hecomes expressed in a modifi- 
cation of the carbohydrate metabolism, leading to the formation of an excluding 
layer of cork; or it may lie in the direction of those substances, as yet so little 
understood, the anti-toxins; or, again, it may be due to still other and eyen less 
apparent causes. But whatever the true nature of the response, it will have to be 
investigated for individual cases, and its secrets will only be unlocked when the 
chemical and physica! processes invulved in its operation are understood. 
In making these remarks I dare say I may be accused of putting forward an 
impossible ideal, or at any rate one that is impracticable of attainment. I am not 
very much concerned about that. Progress is only to be made by trying to 
penetrate further than we can at present see, and I believe we have gained enough 
insight into the chemistry and physics of the living processes to warrant us in 
hoping that we shall penetrate a good deal deeper still. But if we are to ever 
unravel the tangle, it can only be by applying such methods ag have been successful 
in dealing with material things elsewhere. 
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