144 REPORTS ON THE STATE OF SCIENCE.—1918. 
bination of enzyme with urea, and (2) breaking up of the compound, 
the urea being freed in the form of ammonia and carbon dioxide. 
They formulate an expression of two factors, each with an empirical 
constant, which, by proper choice of the two constants, satisfies the 
experimental data. This fact, however, does not prove that the first 
stage is a chemical combination. Indeed, it is stated that the first 
stage, combination between enzyme and urea, is so rapid that no 
appreciable time is lost. If this be so, it is difficult to see why it 
appears in the equation at all. The authors seem to hold that 
physical phenomena, such as adsorption, diffusion and so on, follow 
indefinite laws only. in contradistinction to those of chemical com- 
bination. Further remarks with reference to formulae based on mass 
action alone, will be found below. Although the work in question is 
the most clearly expressed statement of the particular point of view, 
the theory itself is probably the most widely accepted one as applying 
to enzymes. Incidentally, we may remark that the fact that a par- 
ticular reaction appears to follow the ordinary unimolecular law of 
velocity, deduced from mass action, is no guide to the nature of the 
process as a whole. Denham’s (1910) reaction, in which a sheet of 
platinum is the catalyst, follows this law. 
For the first statement of the other view, we must go back to 
Faraday (1834). The experiments and conclusions to be found in 
his paper, ‘On the Power of Metals and other Solids to Induce the 
Combination of Gaseous Bodies,’ are apt to be forgotten, so that I 
make no excuse for referring to them insome detail. The phenomena 
in question are the combination of oxygen (and nitrous oxide) with 
hydrogen, induced by the surface of metallic platinum and other 
solids. In paragraph 619, Faraday states ‘ All the phenomena con- 
nected with this subject press upon my mind the conviction that 
they are dependent upon the natural conditions of gaseous elasticity, 
combined with the exertion of that attractive force possessed by 
many bodies, especially those which are solid, in an eminent degree, 
and. probably belonging to all; by which they are drawn into asso- 
ciation more or less close, without at the same time undergoing 
chemical combination, though often assuming the condition of 
adhesion ; and which occasionally leads, under very favourable 
circumstances, as in the present instance, to the combination of 
bodies simultaneously subjected to this attraction.’ That the phe- 
nomena are regarded as a condensation on the surface, not a solution 
in the substance of the solid, is clear from the reference to hygro- 
metric, bodies which ‘ condense water vapour around or upon their 
surface,’ and are said to be instances of the same power (par. 621). 
The absence of chemical combination with the surface is stated 
clearly in par. 631,‘ The platina is not considered as causing the 
combination of any particles with itself, but only associating them 
closely around it; and the compressed particles are as free to move 
from the platina, being replaced by other particles, as a portion of 
dense air upon the surface of the globe, or at the bottom of a deep 
mine, is free to move, by the slightest impulse into the upper and 
rarer parts of the atmosphere.’ Par. 632 calls attention to a fact 
which is common to adsorption phenomena in general, and is of 
importance in certain effects of retarding agents on enzymes, as we 
