The Ruling c 



we have the sqi 

 nine squares, ea( 

 leukocyte counts 

 The very smalles 

 the triple ruled 1 

 never used for an 

 in a vaccine. It 

 make one of the 



There are 400 

 large squares, th 

 4000 small squar 



The unit in e 

 millimeter. The 



In making a 

 mark 1 1 just abo 



UNIVERSITY OF CALIFORNIA 



MEDICAL CENTER LIBRARY 



SAN FRANCISCO 



FROM THE IIBRARY OF 

 ARTHUR P. KAELBER, M.D. 





B first place, 

 made up of 

 tection with 

 rge squares. 

 :ersection of 

 ;are and are 

 5 of bacteria 

 squares to 



;re are nine 

 There are 



3 the cubic 



ich has the 

 suction we 

 solution of 



fill the pipette to , 



glacial acetic acid in water is most satisfactory. This gives a dilution of 1-20. 



Counting with the 2/3 inch objective all of the highly refractile dots representing 

 leukocytes in one of the i mm. squares at either of the four corners we note the num- 

 ber and mentally multiply by 20 (the number of times the blood was diluted). As 

 the depth of the diluted blood between the ruled surface of the haemacytometer 

 slide and the under surface of the cover-glass is only i/io of a millimeter, we multiply 

 the figure as above obtained by 10 to get the number of cells in a 1-20 dilution of 

 blood in a space of one cubic millimeter. 



Example: Counted 90 leukocytes; 90X20 = 1800X10 = 18,000: equals number 

 of leukocytes in i cubic mm. of blood. 



For red counts we use the red count pipette which has the 101 mark just above the 

 bulb. Taking up blood to 0.5 we draw up the diluting fluid to 101. This gives a 

 dilution of 1-200. Counting the red cells in five of the aggregations of 16 small 

 squares (1/20 mm.) thus having counted 80 small squares we have counted 1/50 

 of the total number of small squares in a cubic mm., there being 4000 small squares 

 in a cubic mm. Consequently the number of red cells in 80 small squares multiplied 

 by 50 and then by the dilution of 200 gives the number of red cells in one cubic 

 mm. of the blood examined. 



It is well to make a second preparation and record the average of the two counts. 



I 



