82 SECTIONAL ADDRESSES 
entity is, or should be, the more peculiar attribute of experimental 
zoology. To some extent it is true that we cannot understand the full 
potentiality of a frog’s musculature until we have a precise knowledge of 
the dynamic properties of a muscle fibre. The fibre is, or appears to be, 
a less complicated system than the muscle which is working in situ, and it is 
tempting to start with the simpler unit and to pass on to the more compli- 
cated systems by a series of apparently logical steps. To a significant 
extent this argument has appealed to experimental zoologists. We start by 
being interested in the organism as a whole, but soon decide to concentrate 
on one specific organ. Eventually the organ gives place to the cell, and 
thence it is an easy step to the bottom of the ladder where we gather 
together to discuss the structure and the functions of living material in 
terms of atoms and molecules. This point of view is of peculiar signifi- 
cance, for, by means of a common language, zoologists, physiologists, 
chemists and physicists have developed, and are continuing to develop, 
a fruitful field of work. It is, however, a field on which it is dangerous 
to tread without adequate safeguards. It is all too easy to over-simplify 
a problem and to ignore the fundamental properties of living matter ; it 
is all too easy to make artificial pearls and cast them before appreciative 
swine. It is, nevertheless, in this field that the foundations of all biology 
eventually may rest, and perhaps the time has come when we should 
review, as impartially as we can, the relationship between the animate 
world of animals and the inanimate world of the physical chemist. 
The application of physical and chemical methods as instruments of 
biological research needs no defence. Its justification is seen in the 
results which have been obtained. During the past twenty-five years 
our knowledge of the living cell, of the respiratory process, and of the 
mechanisms of nerve and muscle fibres has been placed on a high level 
of precision by methods which are identical in type with those used for 
the study of physico-chemical processes in inanimate systems. In so far 
as these results bear on their own peculiar problems, zoologists must 
accept them, and they must influence our conception of the organism as 
a whole. By using appropriate methods we can define the physical 
properties of living matter, but there always remains the possibility that 
the living organism may possess properties of another nature which 
cannot be defined in physical units. 
When, as biologists, we are asked to define our conception of the nature 
or origin of living matter, we must confine ourselves to views which are 
based on the facts of observation. The more accurate and extensive are 
our observational data, the more precise and the more satisfying will be 
our conclusions. The material with which the biologist must deal is of 
extreme diversity and complexity, and we naturally turn to the physical 
world for standards of measurement which will help us to arrange our 
material and to place our observations in a reasonable relationship to each 
other. As I understand it, the age-long discussion between the mechan- 
istic and vitalist schools of thought turns on how far we believe—on the 
basis of observation—that the facts of biology can be sorted out into an 
harmonious and satisfying series without invoking conceptions which are 
found to be unnecessary in dealing with the facts of observation within 
the physical world. The centre of gravity of the problem shifts from 
