152 BACTERIOLOGICAL DIAGNOSIS. 



ESTIMATION OF THE NUMBER OF 

 LEUCOCYTES. 



All the steps are similar to those just described at 

 full length, except that a different diluting fluid is used. 



The diluting fluid is one which destroys ("lakes") 

 the red corpuscles, but does not injure the leucocytes. 

 It consists of a -3 or -5 solution of acetic acid (glacial) 

 in water ; it is better to add a small quantity of methyl 

 violet or gentian violet, so that the leucocytes are 

 stained and thereby rendered more prominent. This 

 solution is best prepared fresh or at any rate kept in 

 a well stoppered bottle. 



The pipette is distinguished from that used for the 

 red corpuscles by its having the number n above 

 the bulb. This indicates that if blood be sucked up 

 to the mark i below the bulb, and diluting fluid up to 

 the transverse mark above the bulb, the dilution will be 

 i in 10, and so on. 



The blood should be sucked up to the mark i if a 

 great excess of leucocytes is not expected. If the case 

 is one of leucocytosis a greater dilution is better, whilst 

 if there is a great excess of leucocytes (such as occurs 

 in severe leucocythaemia) it is best to use the red 

 corpuscles pipette with a dilution of i in 100, but 

 employing the acetic acid diluting fluid. 



In counting the squares a different method has to be 

 employed, as a far greater number of squares must be 

 counted. Either you may count all the squares on the 

 slide and then make a fresh preparation and count all 

 the squares on it ; or you may adopt the following 

 method, which is much quicker and, therefore, since it 



