4 THE PRESIDENTIAL ADDRESS 
Indeterminist respectively. If so the outcome will be of great 
interest. In any case I feel fortunate in a belief that what I have to 
say will not, if rightly appraised, raise the old issues. To claim, as 
I am to claim, that a description of its active chemical aspects must 
contribute to any adequate description of life is not to imply that 
a living organism is no more than a physico-chemical system. It 
implies that at a definite and recognisable level of its dynamic 
organisation an organism can be logically described in physico- 
chemical terms alone. At such a level indeed we may hope ulti- 
mately to arrive at a description which is complete in itself, just as 
descriptions at the morphological level of organisation may be 
complete in themselves. There may be yet higher levels calling 
for discussion in quite different terms. 
I wish, however, to remind you of a mode of thought concerning 
the material basis of life, which though it prevailed when physico- 
chemical interpretations were fashionable, was yet almost as in- 
hibitory to productive chemical thought and study as any of the 
claims of vitalism. ‘This was the conception of that material basis 
as a single entity, as a definite though highly complex chemical 
compound. Up to the end of the last century and even later the 
term ‘protoplasm’ suggested such an entity to many minds. In his 
brilliant Presidential Address at the Association’s meeting at Dundee 
twenty-two years ago, Sir Edward Sharpey-Schafer, after remarking 
that the elements composing living substances are few in number, 
went on to say: ‘ The combination of these elements into a colloid 
compound represents the physical basis of life, and when the chemist 
succeeds in building up this compound it will, without doubt, be 
found to exhibit the phenomena which we are in the habit of asso- 
ciating with the term “life” ’ Such a compound would seem 
to correspond with the ‘ protoplasm’ of many biologists, though 
treated perhaps with too little respect. The Presidential claim 
might have seemed to encourage the biochemist, but the goal 
suggested would have proved elusive, and the path of endeavour has 
followed other lines. 
So long as the term ‘ protoplasm ’ retains a morphological signi- 
ficance as in classical cytology, it may be even now convenient 
enough, though always denoting an abstraction. In so far, how- 
ever, as the progress of metabolism with all the vital activities which 
it supports was ascribed in concrete thought to hypothetical qualities 
emergent from a protoplasmic complex in its integrity or when 
substances were held to suffer change only because in each living 
cell they are first built up, with loss of their own molecular structure 
and identity, ino this complex, which is itself the inscrutable seat 
of cyclic change, then serious obscurantism was involved. 
Had such assumptions been justified the old taunt that when the 
