146 BACTERIOLOGICAL DIAGNOSIS. 



i in ioo ; 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 i in 150 

 or i 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. 



