1918-19.] Reaction Velocity of Sodium Nitrite on Blood. 153 
commenced it proceeded with about the same rapidity in the case of the 
two stronger solutions, and only slightly more slowly in the case of the 
weakest solution. 
Fig. 3. — Effect of the different concentrations of sodium nitrite indicated against the 
curves on 2 per cent, blood solution. 
Ordinates , extinction coefficients; Abscissae, time in minutes. 
Influence of Serum . — It has been mentioned that with dilute solutions 
of sodium nitrite the reaction on the blood, as determined by the appear- 
ance of the methsemoglobin band in the red, was delayed when compared 
with the action on a solution of washed blood corpuscles. Examined by 
the more delicate spectrophotometric method, an earlier appearance of the 
reaction with washed blood corpuscles invariably occurred. The influence 
of the serum was determined by adding definite proportions of the separated 
serum, diluted when necessary with 0'9 per cent, sodium chloride, to a 
solution of washed blood corpuscles. The results of experiments with four- 
hundredth normal sodium nitrite solution are shown in the graph (fig. 4). 
The presence of 25 per cent, of serum completely inhibited the reaction 
with this strength of nitrite within the time of observation ; 2*5 per cent, 
of serum markedly retarded it ; and even an amount of serum less than 
that in defibrinated blood had a delaying action. This retardation was not 
so marked in some experiments, but with fresh serum it was always con- 
siderable. It was immaterial whether the serum was added to the solution 
of blood corpuscles or to the solution of the nitrite before mixing. Heating 
the serum to 67° C. alone or previously mixed with the nitrite solution, 
even boiling the mixed solution, or the addition of a salt of quinine, did 
not influence the reaction. If the serum and nitrite solutions were mixed 
and allowed to stand at room temperature for some hours, less retardation 
of the reaction on adding to a solution of blood corpuscles occurred. And 
it was further noticed that blood serum some days old had less retarding 
effect than fresh serum, and that the same serum kept in the ice-chest 
