CULTURE MEDIA. 51 
are three perforations: one through which the siphon passes, and another 
for a U tube filled with concentrated caustic soda in order to absorb the 
carbon dioxide from all the air which enters the bottle. The third perfora- 
tion is for a by-pass’ which connects with the siphon just above the top of the 
burette and below the cock by which the flow from the bottle is regulated. 
The object of this is to provide for the entrance into the burette, as the solu- 
tion is.allowed to run from it, of air that has passed through the U tube and 
has had its carbon dioxide removed. 
When the manipulation is carried out uniformly in the manner thus de- 
scribed, and with the constant employment of an end-point which has the 
same intensity of color, very satisfactory and closely agreeing results may 
be obtained by this method. 
