598 
DR. A. GAMGEE ON THE ACTION OE NITRITES ON BLOOD. 
III. On the Influence of Nitrites in modifying the Bespiratory Functions of the Blood. 
Under the term respiratory functions of the blood, I mean to include those physical 
and chemical processes which are concerned in the absorption of oxygen by blood, in 
its combination with the blood-colouring-matter, and its retention thereby so as to be 
readily available for purposes of oxidation, as well as those functions and processes which 
are concerned in the formation and evolution of the carbonic acid of the blood. 
If the action which any substance exerts upon any or all of these various physical and 
chemical processes had to be ascertained, the methods of inquiry ought, in my opinion, 
to be equally varied. 
Hitherto the method which has been almost exclusively employed to furnish evidence 
upon the influence which individual medicinal and poisonous substances exert upon 
blood, has consisted in finding out whether their addition to blood influenced the absorp- 
tion of oxygen or the evolution of carbonic acid. For this purpose two samples of blood 
derived from the same source (one of which has been subjected to the action of the poison 
under examination) are brought in contact with the same quantity of oxygen or atmospheric 
air, and after the fluid and gas have been allowed to remain in contact for some time, the 
amount of oxygen absorbed and carbonic acid evolved is ascertained. This is done by 
determining, first, the contraction which the fluid has undergone, and, secondly, the 
amount of carbonic acid, nitrogen, and oxygen present in the gas after contact. Were 
it easy to place the blood under precisely similar circumstances in the two cases, the evi- 
dence yielded by the method would be very much greater than it really is. In order to 
ensure a very marked action of the blood upon the air, they must be brought together by 
agitation; the violence and the length of time during which this is continued are 
circumstances having the most marked influence upon the rapidity and amount of gaseous 
interchanges which take place. The difficulty of securing the same degree of agitation 
is very considerable, and probably introduces one of the chief errors attaching to this 
method of experimenting. 
In such experiments I believe it to be most essential that the total volume of gas re- 
maining after the experiment, and any contraction or dilatation which may have 
occurred, should be determined with the greatest accuracy. Some experimenters have 
not considered this essential ; for in experiments to test the influence of poisonous agents 
on blood, they have merely made percentage analyses of the air after contact. 
A second method which suggests itself as most valuable in investigating the action of 
poisonous agents upon the respiratory functions, is based upon the property which car- 
bonic oxide gas possesses of displacing the oxygen of blood. The normal condition of 
the colouring-matter will obviously be tested in a valuable manner if we agitate it 
thoroughly with air and oxygen, and then bring it in contact with carbonic oxide gas. 
If the gas displaces as much oxygen from the poisoned blood as from normal blood which 
has been under exactly the same circumstances, we shall have evidence to show that 
the addition of the poison has, first, not prevented the normal absorption of oxygen ; 
secondly, has not removed the oxygen from the blood by a special chemical action of its 
