PRESIDENTIAL ADDRESS. 667 
of the cell present a side to which the considerations I have put before you 
do not apply. Paul Ehrlich, in his recent illuminating address to the Inter- 
national Congress of Medicine, remarked that if, in chemistry, it be true that 
Corpora non agunt nisi liquida, then, in chemiotherapy, it is no less true that 
Corpora non agunt nisi fixata. Whatever precisely may be involved in the 
important principle of ‘fixation’ as applied to drug actions, it remains, I 
think, true that the older adage applies to the dynamic reactions which occur 
in the living cell. But there are doubtless dynamic phenomena in which the 
eell complexes play a prominent part. ‘he whole of our doctrine concerning 
the reaction of the body to the toxins of disease is based upon the fact that 
when the cell is invaded by complexes other than those normal to it, its own 
complexes become involved. I must not attempt to deal with these phenomena, 
but rather proceed to my closing remarks. I would like, however, just to 
express the hope that the chemist will recognise their theoretical importance. 
He wiil not, indeed, be surprised at the oligo-dynamic aspects of the phe- 
nomena, startling as they are. When physico-chemical factors enter into + 
phenomenon the influence of an infinitely small amount of material may always 
be expected. It is a fact, for instance, as Dr. W. H. Mills reminds me, that 
when a substance crystallises in more than one form it may be quite impossible 
to obtain the less stable forms of its crystals in any laboratory which has been 
‘infected’ with the more stable form, even though this infection has been 
produced by quite ordinary inanipulations dealing with the latter. Here, 
certainly, is a case in which the influence of the infinitesimal is before us. But 
what I feel should arrest the interest of the chemist is the remarkable mingling 
of the general with the particular which phenomena like those of immunity 
display. In the relations which obtain between toxin and anti-toxin, for 
example, we find that physico-chemical factors predominate, and yet they are 
associated to a high degree with the character of specificity. The colloid state 
of matter, as such, and the properties of surface determine many of the 
characteristics of such reactions, yet the chemical aspect is always to the front. 
Combinations are observed which do not seem to be chemical compounds, but 
rather associations by adsorption; yet the mutual relations between the inter- 
acting complexes are in the highest degree discriminative and specific. The 
chemical factor in adsorption phenomena has, of course, been recognised else- 
where; but in biology it is particularly striking. Theoretical chemistry must 
hasten to take account of it. The modern developments in the study of valency 
probably constitute a step in this direction. 
It is clear to everyone that the physical chemist is playing, and will continue 
to play, a most important part in the investigation of biological phenomena. We 
need, I think, have no doubt that in this country he will turn to our problems, 
for the kind of work he has to do seems to suit our national tastes and talents, 
and the biologist just now is much alive to the value of his results. But I 
rather feel that the organic chemist needs more wooing and gets less, though I 
am sure that his aid is equally necessary. In connection with most biological 
problems, physical and organic chemists have clearly defined tasks. To take 
one instance. In muscle phenomena it is becoming every day clearer that 
the mechanico-motor properties of the tissue, its changes of tension, its con- 
traction and relaxation, depend upon physico-chemical phenomena associated 
with its colloidal complexes and its intimate structure. Changes in hydrogen- 
ion concentration and in the concentration of electrolytes generally, by acting 
upon surfaces or by upsetting osmotic equilibria, seem to be the determining 
causes of muscular movement. Yet the energy of the muscle is continuously 
supplied by the progress of organic reactions, and for a full understanding of 
events we need to know every detail of their course. Here then, as everywhere 
else, is the need for the organic chemist. 
But I would urge upon any young chemist who thinks of occupying himself 
with biological problems, the necessity for submitting for a year or two to a 
second discipline. If he merely migrate to a biological institute, prepared to 
determine the constitution of new products from the animal and study their 
reactions in vitro, he will be a very useful and acceptable person, but he will 
not become a bio-chemist. We want to learn how reactions run in the organism, 
and there is abundant evidence to show how little a mere knowledge of the 
constitution of substances, and a consideration of laboratory possibilities, can 
help on such knowledge. The animal body usually does the unexpected. 
