156 Proceedings of the Royal Society of Edinburgh. [Sess. 
minutes. The effect of larger concentrations of sodium hydroxide is seen 
in the figure. 
The experiments made seem to show that the minimal amount of sodium 
hydroxide necessary to lengthen the induction period of the reaction bears 
some proportion to the amount of sodium nitrite. For four-hundredth 
normal nitrite it is about ten-thousandth normal sodium hydroxide, and 
for two-hundredth normal nitrite about four-thousandth normal sodium 
Fig. 7. — Effect of concentration of sodium hydroxide indicated against the 
curves on the reaction between twentieth normal sodium nitrite and 
0'5 per cent, solution of washed blood corpuscles.- 
Ordinates, extinction coefficients ; Abscissae, time in minutes. 
hydroxide ; for twentieth normal nitrite it is about two-thousandth normal 
sodium hydroxide. With concentrations below this minimal strength no 
effect is produced. As the strength of alkali is increased above the 
minimum, the result, at first, is one of prolongation of the induction period, 
and it is only after the concentration has been considerably increased that 
the reactionary period itself is influenced. Even relatively concentrated 
alkali does not inhibit the reaction provided a concentrated solution of 
sodium nitrite is also used. Thus twentieth normal sodium nitrite reacts 
with a solution of blood in the presence of fortieth normal sodium 
hydroxide. The reaction, however, is so slow that its course has not been 
followed. This fact would seem to dispose of the idea that the reaction 
is dependent on the formation of nitrous acid. The presence of acid 
undoubtedly powerfully accelerates the reaction : the acceleration is dis- 
tinctly noticeable with solutions of blood in four-thousandth normal acetic 
acid. But urea has no influence on the reaction. This proceeds in the 
presence of 25 per cent, urea, both in acid and alkaline solutions, as if the 
urea were not there. The mode of action of sodium nitrite on blood will 
be dealt with in a future communication. 
(Issued separately October 20 , 1919 .) 
