146 BACTERIOLOGICAL DIAGNOSIS. 
1 in 100; if he has approximately the normal number of 
corpuscles, or if you have reason to think that they be 
present in increased quantities, use a dilution of 1 in 150 
or 1 in 200. 
Having decided upon the degree of dilution insert the 
tip of the pipette into the drop of blood lying on the 
skin, take the bone mouth-piece attached to the india- 
rubber tube in your mouth, and suck the blood up to 
the appropriate mark. If air bubbles gain access blow 
the blood out and begin again. If you over-shoot the 
mark remove some of the blood by touching the tip of 
the pipette against some absorbent cotton-wool. Now 
remove the pipette from the blood and wipe off the 
excess with your finger; prevent blood from flowing 
out by placing the tip of your tongue in the aperture 
of the bone mouth-piece. Place the tip of the pipette 
in the diluting fluid; a small quantity should be poured 
out into a watch-glass or other suitable vessel, so as to 
avoid any possibility of allowing some blood to escape 
into the stock bottle and invalidating a subsequent obser- 
vation. Suck the diluting fluid slowly into the pipette 
until it reaches the single mark above the bulb; it is 
best to rotate the pipette between the finger and thumb 
as you do so. 
Now remove the pipette from the diluting fluid, pre- 
venting escape of fluid from the bulb by placing the tip 
of the tongue on the aperture of the mouth-piece as you 
do so; then place the tip of the finger over the aperture 
of the pipette (fig. 23, S) and proceed to mix the con- 
tents by rotating the pipette and by turning it over and 
over. It is hardly necessary to say that it is useless to 
shake it. 
If the examination is to be made at a distance remove 
the india-rubber tube and stretch an india-rubber band 
so as to close both apertures of the pipette. 
