148 REPORTS ON THE STATE OF SCIENCE.—1918. 
there is only one case in which evidence of-a kind of intermediate 
compound of a chemical nature has been brought forward. So far as 
I am aware, no compound between enzyme and substrate has been 
shown to exist. Adsorption compounds or colloidal complexes have 
been obtained when the substrate is in the colloidal state, as between 
starch and amylase, and between trypsin and casein. But such com- 
pounds are formed whether the substrate is one capable of attack by 
the enzyme or not. Thus, amylase forms a similar compound with 
casein and with starch, and it appears to be a mere physical juxta- 
position of the colloidal particles, held together by mechanical or 
electrical forces. 
A certain amount of evidence that adsorption alone can increase 
the rate of change is afforded by some experiments which the present 
writer made with powdered charcoal and urea solution. Urea in 
solution, as Walker and Hambly (1895) showed, is slowly changed 
into ammonium cyanate, up to a certain equilibrium position. This 
is followed by a further change into ammonium carbonate. The 
rate of this change is accelerated to a marked degree by the presence 
of powdered charcoal. 
The absence of an intermediate compound is more definitely in- 
dicated in the investigation of Horace Brown (1914) on some Cape 
wines, where an oxidation proceeds under the influence of a catalyst 
consisting of iron in the ferrous state associated with tannin and 
protein. This acts asa ‘carrier of oxygen,’ as in Fenton’s reaction. 
The observations of Moore and Webster (1918) on the photosynthesis 
of formaldehyde in presence of inorganic colloids are also to the 
point. They show that the effects are not due to changes of the 
catalyst from a higher to a lower oxide, but to a surface condensation 
of carbon dioxide on the particles. The effect is given indeed by 
silicic acid, in addition to ferric and uranic hydroxides and beryllium 
chloride, also, to a less extent, by copper, nickel, palladium, man- 
ganese and erbium salts. The bearing of this fact on the problem of 
chlorophyll assimilation in plants is obvious. It suggests that the 
function of the pigment in the chloroplasts is to absorb light energy 
which is then utilized by the aid of an-iron catalyst to reduce 
carbonic acid to formaldehyde. 
Tt has been pointed out to me by Prof. Hopkins that if the pro- 
cess is to be regarded as the rapid attainment of the natural equilibrium 
in consequence of condensation on the surface of the enzyme, it 
follows that all the constituents of the system must be adsorbed in 
the same relative proportion as in the body of the liquid, otherwise 
there must be a change in the equilibrium position. I have made 
some experiments to test this deduction, but the difficulties are great 
and the work is for the present interrupted. I found, however, that 
a mixture of ethyl alcohol, acetic acid, ethyl acetate and water, after 
equilibrium had staken place, was unaltered by the addition of 
powdered charcoal, although charcoal is known to adsorb some of 
the constituents, at all events. The result indicates that the various 
constituents must have been adsorbed in the same proportion as that 
in which they were present in the mixture. But further experi- 
ments are desirable and it does not follow that enzymes behave like — 
charcoal. Curiously enough, it appears to be well established that, — 
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