50 
Proceedings of Royal Society of Edinburgh. [sess. 
cumstances., so often remarked. The need for that stage of growth 
outside the body and the influence of the “ time ” and “ place ” 
disposition as affecting this becomes thus more readily understood. 
It is not denied that many other factors, such as personal predis- 
position, and all conditions local or seasonal which favour a state of 
intestinal irritation, come also into play ; but to discuss these at 
present would be obviously out of place. It is sufficient to have 
noted that we have here a factor in this question which has not as 
yet received consideration. 
The whole question of enzyme action is of profound interest, 
from a general physiological point of view. Burdon Sanderson 
has recently advised us to study function, not in its simplest, 
but in its most specialised form. Contractility is not to be investi- 
gated in a mass of undifferentiated protoplasm, but in striped muscle. 
We have in the case of the enzymes a function of the organism, 
separable from the protoplasm, whose mode of action we can investi- 
gate at our leisure. It is a catabolic function of the organism, and 
by a complete knowledge of its mode of action we should learn how 
the process of combustion in the animal body proceeds at so low a 
temperature. The action of enzymes is generally recognised as con- 
sisting in a splitting up of complex molecules into simpler, accom- 
panied by hydration. The same result is attained by the chemical 
action of acids and alkalies or even by a much higher temperature 
alone. Thus hydrochloric acid can convert fibrin into peptone and 
starch into sugar. But this occurs only at 100° C., whereas with 
enzymes the change takes place at a very much lower temperature. 
The power possessed by a comparatively small quantity of an enzyme 
of decomposing relatively very large quantities of a special medium 
is spoken of as due to catalytic action — an action bordering on the 
chemical and the physical. The dependence of its optimum action 
on a definite temperature suggests that it may consist in the trans- 
mission of a certain molecular motion, which enables the molecule 
to be decomposed at a much lower temperature than if the force 
were less accurately adjusted to the work to be performed, — just as 
certain chemical substances explode most readily when sound waves 
of a certain length and rapidity impinge on them, or as certain rays 
of light decompose or cause to combine certain chemical bodies. The 
energy which is present in the shape of temperature, instead of acting 
