SPECIAL BACTERIOLOGY 
123 
centimeter. With a blood lancet prick a finger and draw 
blood into a capillary pipette for a distance of one inch 
(marked with red pencil) ; a little air is then allowed to 
enter and then the bacterial emulsion is drawn up to the 
same mark. We now have equal amounts of blood and bac¬ 
teria; these are thoroughly mixed by alternate drawing 
in and out of the contents of the pipette on a watch- 
glass. Then smears are made of this mixture on a glass 
slide in the same manner as blood smears; put a large 
drop of the mixture on a glass slide and with another 
glass slide resting on the drop make a quick rapid 
smear. Stain with Wright’s stain (see section on 
Staining) ; count several fields, counting red blood cells, 
and bacteria. Let us suppose that we counted altogether 
300 red blood cells and 150 bacteria. That means there are 
twice as many red blood cells as bacteria. Since there are 
5,000,000 red blood cells in a cubic millimeter of normal 
blood, our vaccine (which contains half as many bac¬ 
teria as there are red blood cells) contains 2,500,000 bac¬ 
teria per cubic millimeter, or 2,500,000,000 per cubic 
centimeter. Now if we do not want our vaccine to be 
so concentrated, we can dilute it with salt solution to 
the desired concentration. 
The vaccine is now taken out of the water-bath, 
poured into a sterile graduated cylinder, enough salt 
solution is added to bring it to the desired concentration, 
and 0.25 per cent of tricresol is added, and the vaccine 
is allowed to stand at room temperature overnight; next 
morning aerobic and anaerobic cultures are made, and if, 
in forty-eight hours, no evidences of contamination are 
seen, the vaccine is poured into small ampoules and 
sealed. 
