ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS, 151 
V. The Transport of Gases in Animals. 
Oxygen is continually being used up and carbon dioxide produced 
by the oxidation of food materials in the tissues of animals. When 
the current of blood flowing ina given time is compared with the 
consumption of oxygen and the carbon dioxide produced in the same 
time it is clear that, in neither case, is the amount that could be 
carried in solution in the liquid of the blood nearly sufficient to 
account for that actually transported. 
Both these gases, therefore, must be carried in some kind of 
combination with substances present in the blood. It will clear the 
way if we exclude certain possibilities at once. Oxygen is taken up 
by the blood in the air sacs of the lungs, where its partial pressure is 
about 100 mm. of mercury. The venous blood has an oxygen tension 
of about 37mm. of mercury. Accordingly, the substance serving 
for the transport of oxygen must be one which takes up oxygen 
when exposed to a tension of this gas of 100mm. and gives it off 
again, more or less completely, at 37 mm. or thereabouts. The 
tension of carbon dioxide in the lungs is 40 mm. of mercury ; in the 
blood arriving from the tissues about 64mm. or thereabouts. The 
substance transporting this gas must be one that takes up carbon 
dioxide at 64mm. and gives it off at 40mm. There is only one 
substance present in the blood that has the requisite properties as 
regards oxygen, that is the red colouring matter of the red blood 
corpuscles, hemoglobin. This has been known fora long time. But 
some confusion has arisen with regard to carbon dioxide, because 
sodium bicarbonate is present in the blood plasma, and it was natural 
to look upon this as the carrier. Bohr (1891), however, had already 
shown that sodium bicarbonate gives off no carbon dioxide to the 
gas at a pressure of 40mm. of mercury, and Buckmaster (1917) has 
confirmed this statement. The latter observer has also shown that 
there is no substance present in the blood acting as an acid to drive 
‘off the carbon dioxide. There seems to be no possibility of a dis- 
sociable compound of carbon dioxide with ihe proteins of the blood 
plasma. We have seen that proteias do not combine with weak acids, 
although a process akin to adsorption may occur, although it is not 
definitely shown to be present. The part played by the proteins is 
as yet somewhat uncertain, but the work of Buckmaster has proved 
that by far the greater part of the carbon dioxide, if not all, is carried 
by the hemoglobin in a manner similar to that in which it carries 
oxygen. 
The function of the sodium bicarbonate, as Lawrence Henderson 
(1908) has so well shown, is to preserve the hydrogen-ion concen- 
tration of the blood within narrow limits. 
' The work of Barcroft and his coadjutors has brought out in+ 
detail the relations between oxygen and hemoglobin, under various 
conditions, and shown how the facts can be expressed in a mathe- 
‘matical form. A complete account will be found in Barcroft’s book 
(1914). The object of the present report is to point out the difficulties 
met with when an attempt is made to reconcile the interpretation 
sometimes given to these expressions with the fact that hemoglobin 
exists in the blood as a heterogeneous phase, In the corpuscles the 
