PRESIDENTIAL ADDRESS. 445 
hydrolytic disruption under its influence, the asymmetric centre being that at 
which the cleavage is effected. 
In synthetic changes the operation is reversed. It may be supposed that 
the separation of hydrone is determined by the circumstance that water can 
be formed by the interaction of this hydrone as it separates with that which 
is attached to the hydrolated enzyme; the formation of water from hydrone, 
in fact, plays a great part in such changes. 
The action of oxydases may be regarded from a similar point of view. 
The early observations of Adrian Brown on the oxidising activity of 
Bacterium Xylinum, coupled with the later work of Bertrand, affords clear 
proof that these enzymes are possessed of selective powers. It is conceivable 
that such enzymes become attached to a molecule at some one centre and 
that they then deliver their attack at some more or less distant point by 
presenting the oxygen with which they are loosely associated at this point. 
It is easy, on such an assumption, to understand how ethenoid linkages may 
be developed in various positions in the molecule of a fatty acid. 
Rosenthaler’s recent observations on the formation of optically active 
phenylhydroxycyanomethane, PhCH(OH)CN, from hydrogen cyanide and 
benzaldehyde on shaking the solution with emulsin are, however, among 
the most significant yet made. I have myself confirmed his statements. 
The ease with which the change takes place—the manner in which the 
change is accelerated by the enzyme—is altogether remarkable. 
Although there can be little doubt, in the case of plants and animals, 
that the synthetic processes do not occur spontaneously and directly between 
the interagents but are for the most part at some stage or other directed 
or controlled, it cannot well be supposed that every asymmetric compound 
is the direct outcome of a controlled process ; nor is it necessary to assume 
that such is the case. Not a few asymmetric compounds are probably but 
secondary products formed by the breakdown of compounds which are the 
products of directed synthesis. 
Ehrlich’s observations on the formation of the amylalcohols from the 
isomeric aminocaproic acids (leucines) may be referred to in this connexion. 
Taking into account the manner in which the vegetable organism is pro- 
vided with conservative powers and its tendency to retain nitrogen, in view 
of the peculiar structure of the members of the terpene group—especially the 
presence of the isopropyl group and of methyl in association with the ring 
in <uch hydrocarbons—it is highly probable that the terpenes are derived 
from amino-acids. A molecule of leucine, a molecule of alanine, and a 
molecule of formaldehyde obviously provide the materials for the production 
of methylisopropyldihydrobenzene ; it is not difficult to picture the series 
of changes which would lead to the formation of the hydrocarbon from such 
a conjunction. 
The general impression produced by facts such as have been referred to 
is that directive influences are the paramount influences at work in building 
up living tissues. These come into operation, it is to be supposed, at a very 
early stage in the case of the plant. The initial step probably involves the 
electrolysis of water under the influence of solar energy and the reduction by 
the hydrogen thus liberated of the carbon dioxide, which is eventually 
converted into formaldehyde, either directly or, it may be, through the 
intermediation of oxalic and formic acids. The part which chlorophyll 
plays in this process can only be surmised : it is not improbable that reduced 
chlorophyll is the active reducing-agent: that chlorophyll itself is active 
in conditioning the resolution of water under the influence of solar energy 
into reduced chlorophyll and oxygen or, more probably, a labile peroxide, 
from which oxygen is independently split off at a subsequent stage, it may 
be under the influence of a so-called catalase. 
Whatever the process by which the plant acquires its initial store of 
‘carbonaceous material, the formaldehyde is apparently at once made use of 
