2 THE PRESIDENTIAL ADDRESS 
not claiming it here, that in studying Life we soon meet with aspects 
which are non-metrical. I would have you believe, however, that 
the data of modern Biochemistry which will be the subject of my 
remarks were won by quantitative methods fully adequate to justify 
the claims based upon them. 
Though speculations concerning the origin of Life have given 
intellectual pleasure to many, all that we yet know about it is that 
we know nothing. Sir James Jeans once suggested, though not 
with conviction, that it might be a disease of matter—a disease of 
its old age! Most biologists, I think, having agreed that Life’s 
advent was at once the most improbable and the most significant 
event in the history of the Universe, are content for the present to 
leave the matter there. 
We must recognise, however, that Life has one attribute that is 
fundamental. Whenever and wherever it appears the steady 
increase of entropy displayed by all the rest of the Universe is then 
and there arrested. There is no good evidence that in any of its 
manifestations life evades the second law of thermodynamics, but 
in the downward course of the energy-flow it interposes a barrier 
and dams up a reservoir which provides potential for its own re- 
markable activities. The arrest of energy degradation in living 
Nature is indeed a primary biological concept. Related to it, and 
of equal importance is the concept of Organisation. 
It is almost impossible to avoid thinking and talking of life in this 
abstract way, but we perceive it, of course, only as manifested in 
organised material systems, and it is in them we must seek the 
mechanisms which arrest the fall of energy. Evolution has estab- 
lished division of labour here. From far back the wonderfully 
efficient functioning of structures containing chlorophyll has, as 
everyone knows, provided the trap which arrests and transforms 
radiant energy—fated otherwise to degrade—and so provides power 
for nearly the whole living world. It is impossible to believe, 
however, that such a complex mechanism was associated with life’s 
earliest stages. Existing organisms illustrate what was perhaps an 
earlier method. ‘The so-called autotrophic bacteria obtain energy 
for growth by the catalysed oxidation of materials belonging wholly 
to the inorganic world; such as sulphur, iron or ammonia, and 
even free hydrogen. These organisms dispense with solar energy, 
but they have lost in the evolutionary race because their method 
lacks economy. Other existing organisms, certain purple bacteria, 
seem to have taken a step towards greater economy, without reaching 
that of the green cell. ‘They dispense with free oxygen and yet 
obtain energy from the inorganic world. They control a process in 
which carbon dioxideis reduced and hydrogen sulphide simultaneously 
oxidised. ‘The molecules of the former are activated by solar energy 
