l88 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



squares, twenty along each side. You have to count at least a 

 hundred of these small squares. The simplest way to do this is 

 to count five " bars " of twenty each, each bar extending right 

 across the ruled " chess-board." The bars selected should be as 

 far as possible apart from one another, so as to get a good 

 average. In practice it is simplest to take the top one, and all 

 the others that have a double ruling ; when you have counted 

 these you will have counted five rows of twenty each at equal 

 distances from one another, which will give you a very fair 

 average. (See Fig. 46, where the bars which are to be counted 

 are shaded.) 



Fig. 47. — Showing Method of Counting Red Corpuscles. 



a, a, a, are counted in square A ; 6, 6, in B ; c in C. In this method each 

 corpuscle is counted once, and once only. 



In counting these bars count all the corpuscles which are lying 

 on or touching the top line, as in the bar you are counting, also 

 those which are lying on or touching the extreme left-hand 

 limit of the bar. Exclude those on or touching the lower and 

 right-hand lines. The reason for this will appear subsequently. 



This is the most convenient way when you have no assistant 

 to take down numbers, since you only have to remove your eye 

 from the microscope for the purpose of recording results five 

 times in the whole process, which takes about five minutes or 

 less. It is, however, rather more accurate to take down the 

 count square by square, dictating the number to an assistant, who 

 tells you when you have counted a hundred ; you are less likely 



