88 



STUDENTS HISTOLOGY 



particles or fluid should separate the cover-glass from the surface of the square 

 of glass surrounding the disk. 



The disk is depressed -n> mm. below the upper surface of the square. 

 It is also ruled into 400 squares -^ mm. on each side. When the blood- 

 corpuscles fall to the surface of the di^k, as they do after a few minutes, the 

 number counted in one square represents those present in Tcfoo" cu.mm. of 

 the diluted blood. UVX a^X TO-) Every fifth square is crossed by a second 

 ruled line, which encloses the small squares into groups of sixteens and assists 

 in counting. Using the high-power, tne corpuscles in a given number of 

 squares in various parts of the plate are counted. In counting, discard the 

 corpuscles that touch the lines on two sides (above and at the right), and 



FIG. 63. APPEARANCE OF FIELD OF HJEMOCYTOMETER 

 UNDER HIGH-POWER. (FREEBORN.) 



count those that touch the other two (below and at the left); the average for 

 one small square is thus taken. It is best to wipe away the first drop after 

 a number of squares have been counted, replacing it with another, after 

 thoroughly shaking the pipette. In all, count the number in about four 

 hundred small squares. Multiply the average number for one square by 4,000 

 and by the dilution (100 or 200), and the number of red (or white) corpuscles 

 in a cubic millimeter of blood is obtained. 



The number of red blood -corpuscles in a cu.mm. of human 

 blood is 5,000,000, or somewhat more, for men, and about half a 

 million less for women. The normal number of white corpuscles 

 is from 5,000 to 10,000 in a cu.mm. 



