152 REPORTS ON THE STATE OF SCIENCE.—1918. 
concentration of hemoglobin is about 30 per cent. No solution of 
hemoglobin of this strength can be made. Even in 4 per cent. it 
forms a colloidal suspension, and it does not diffuse through parchment 
paper, however dilute the solution may be. 
Barcroft explains the phenomena on the basis of chemical com- _ 
bination between oxygen and hemoglobin, a series of compounds, 
HbO., Hb,O,, Hb,0,, &c., being formed in different relative pro- 
portions according to the electrolytes present in the solution. These ~ 
electrolytes are regarded as causing aggregation of hemoglobin 
molecules; the aggregate Hb,, when it combines with two molecules 
of oxygen, leads, by mass action, to a different order of equation 
from that of Hb and O., which is unimolecular. But it is not yet 
certain that we are justified in applying the law of mass action in a 
simple form to heterogeneous systems and, if we apply the phase 
rule, we are at once met with difficulties, as will be seen below. On 
the other hand, it is not universally accepted that the phase rule 
‘ean be applied to colloidal solutions, although the hemoglobin in 
the corpuscles may reasonably be regarded as a more definitely 
distinct phase. 
Barcroft’s experimental results are of so much value that it seems 
to the writer that there is some risk of the problem being prematurely 
considered to be solved and the very remarkable character of the 
phenomena being overlooked. 
Assuming that the phase rule applies, what does it tell us? If 
HbO, is a chemical compound, there are three phases present in a 
solution of it when in contact with an oxygen atmosphere, Hb, HbO: 
and oxygen. There are two components; because Hb and Hb0, vary 
inversely; the oxygen is present in unlimited amount. There is 
therefore only one degree of freedom: 
F=C+2—P=24+2-—-3=1. 
In other words, at a given temperature, say that of the blood, the 
whole of the hemoglobin is either reduced or oxidized, according to 
the tension of the oxygen. Bui this is not the case. It is well 
known that hemoglobin varies in its content in oxygen, at the same 
temperature, according to the tension of oxygen. It is free from 
oxygen at zero tension and saturated at about 100 mm. of mercury at 
the temperature of 38° C., while it follows a particular law, expr essed 
by the dissociation curve, ” between these values. 
Apart from this deduction from the phase rule, there are obniaie 
chemical systems that have been hastily assumed to be similar to that 
of oxygen and hemoglobin. We shall see that they are different and 
really obey the phase rule. 
By a misunderstanding of Le Chatelier’s data (1883), the chicraan 
_ oxide and carbon dioxide 1 system has been supposed to throw light 
on the hemoglobin question. But, at a given temperature, the 
calcium is present either entirely in the form of calcium oxide or 
‘calcium carbonate, according to the tension of carbon dioxide. At 
tensions below a certain value, different for each temperature, we 
have complete decomposition ; at all tensions above this value, the 
whole exists as calcium carbonate, and there are no intermediate 
stages. At first sight, again, a solution of sodium bicarbonate in 
water seems more like the one we seek. At tensions of carbon 
