666 
NATURE 
[May 19, 1923 
Ss 
Letters to the Editor. 
[Zhe Editor does not hold himsel) responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, nor to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of NATURE. No notice is 
taken of anonymous communications. | 
Adsorption and Hemoglobin. 
As I have in other places entered a plea for more 
consideration of the possibility that adsorption may 
play some part in the phenomena of the taking up of 
oxygen by hemoglobin, a few remarks on the letter 
by Mr. N. K. Adam in Nature of April 14 may be 
permitted me, chiefly with the object of making clear 
my attitude in the matter. It is briefly this. Nearly 
all, if not all, of the workers on the problem direct 
their attention only to the investigation and inter- 
pretation of these phenomena from the point of view 
of mass action in a homogeneous system. Now, while 
this may ultimately turn out to be the correct view, 
it must not be overlooked that hemoglobin under 
most conditions exists in the form of colloidal aggre- 
gates. Thus, surface phenomena may intervene and 
should receive due consideration, even if only to be put 
on one side. This has not been attempted to any 
serious extent, since Wo. Ostwald showed that the data 
of the taking up of oxygen by hemoglobin could. be 
expressed by an adsorption formula. It is true that 
such a formula, as Mr. Adam says, contains two 
arbitrary constants, and fitting it to the experi- 
mental data does not prove anything as to the nature 
of the phenomena. But the same statements may 
be made with regard to the widely accepted Barcroft- 
Hill expression. 
Any criticism that I venture to make is not to be 
understood as doubting the value of the data that 
are being obtained, but rather as directing attention 
to certain gaps in our knowledge which require to be 
filled up before further progress in the interpretation 
of the facts can profitably be made. There is, as it 
seems to me, some risk of building elaborate hypo- 
theses on assumptions which are not clearly demon- 
strated. It appears sometimes that workers are so 
convinced that the mass action view is all that is 
necessary, that they are not interested in testing the 
truth of these assumptions. If it is found that an 
experimental result can be explained on the lines of 
mass action formule, however elaborate, it is taken 
as confirming the view ; but other hypotheses might 
be found equally well to satisfy the case, if seriously 
examined. Compare, for example, Langmuir’s for- 
mulz for the adsorption of a gas by a crystal surface 
with the Hill-Barcroft formula. I am sometimes in- 
clined to wish that it were possible for an investigator 
who knew nothing about previous theories to attack 
the problem as a new one. 
But to be more precise—it is undoubtedly a very 
important fact that when hzmoglobin has taken up 
all the oxygen that it can, this oxygen is in the 
proportion of one molecule to each atom of iron in 
the molecule of hemoglobin. It is natural to believe 
that the iron and oxygen are directly united. Mr. 
Adam’s assumption that the oxygen is “ locally 
attracted ”’ rests on this belief. Are we quite certain 
that it is the case? And even if it were, we know 
too little about the forces which bring about adsorp- 
tion to be able to exclude the possibility of local 
foci, as it were. On the view of chemical combina- 
tion, in the strict sense, between oxygen and iron, is 
not the greater affinity of hemoglobin for carbon 
monoxide than for oxygen rather puzzling? There 
is also the problem of methemoglobin, another com- 
NO. 2794, VOL. 111] 

pound of hemoglobin and oxygen, but one which does 
not give up its oxygen toa vacuum. I have not been 
able to find in the literature dissociation curves of 
oxyhemoglobin continued beyond the saturation 
point in the presence of excess of salts or of carbon 
dioxide. On the purely chemical theory, with suffi- 
cient concentration of oxygen, the saturation point 
should still be in the same proportion of iron to 
oxygen. In connexion with the relations between — 
hemoglobin and carbon dioxide, no proof has yet 
been given that the union is of a different nature 
from that with oxygen. It is still uncertain whether 
the hemoglobin that combines with carbon dioxide is 
a sodium salt. ‘ 
To put the question in another way—-does hemo- 
globin free from sodium combine with carbon dioxide, 
or does it not? But if hemoglobin, as worked with, 
is a sodium salt, osmotic pressure measurements give 
no direct information as to the molecular weight of 
hemoglobin. It appears to be accepted by most of — 
those working on the problems that oxyhzemoglobin is 
a much stronger acid than hemoglobin itself. Itis true 
that to explain the carriage of carbon dioxide by mass 
action formule, this is necessary. But is it impossible 
to put the question to more satisfactory experimental 
test than has yet been done? Again, the cause of 
the widely divergent results obtained by different 
| investigators of the heat of combination between 
oxygen and hemoglobin has not been adequately 
made out. While, therefore, the data which are being 
accumulated in so many places are of the greatest 
value in relation to the actual behaviour of hamo- 
globin under certain conditions, I find it impossible 
to interpret them on the basis of any theory until the 
questions above mentioned are answered. - 
A subsidiary point, but one about which agreement 
is desirable, is the use of the name ‘‘ polymerisation ” 
in place of the more usual one, in relation to colloidal 
behaviour, of “ aggregation.’’ It would be of advan-— 
tage if clear definition of these terms, together with 
that of “ association,” could be agreed upon. : 
It is perhaps to the point to recall those processes 
which obey the unimolecular law as deduced from 
mass action, at all events in a part of their time 
course, although we know that as a whole they are 
much more complex than simple chemical combina- 
tions. 
Turning to Mr. Adam’s criterion of adsorption, I 
agree that it is impossible to define it by the nature 
of the forces concerned. It seems to me, however, 
that it is only shown when a sufficient number of 
atoms are joined to form a surface. To adopt the 
criterion of the whole surface becoming uniformly 
covered when the concentration rises to a certain value, 
neglects, I think, those cases where two or more 
substances are adsorbed simultaneously. Mr. Adam 
appears to accept Langmuir’s views. While these 
explain many cases, there are others where the range 
of the forces concerned extends beyond one molecule. 
According to Evans and George (Proc. R.S., A, 103, 
p- 192) the thickness of the layer of carbon dioxide 
on glass amounts to that of five or six molecules. 
Chemical forces in the ordinary sense seem te be 
excluded here. Moreover, accepting the probability 
of orientation on an inert surface, like that of char- 
coal, by affinity of certain groups for the water of 
the liquid phase, it is difficult to see how the increased 
concentration itself is initially brought about. But, 
after all, is it not rather an idle discussion to make 
definite distinctions between chemical and physical 
forces in the region of atomic properties ? Does not 
the Braggs’ crystal model indicate that the forces 
responsible for cohesion, chemical union, and elec- 
trical behaviour are one and the same? The recent 


