MICROMETRY AND BLOOD PREPARATIONS 



Having brought the lines on the stage micrometer to a focus, we determine the 

 number of spaces on the stage micrometer which the 50 divisions of the ocular 

 micrometer cover. To distinguish the ruling of the ocular from that of the stage 

 micrometer, revolve the ocular with the fingers. 



The tube length which is used at the time of standardizing must 

 always be adhered to in subsequent measurements. 



FIG. 51. Micrometry diagrams, i. Ocular micrometer with stage micrometer. 

 50 spaces of ocular micrometer cover two zoo-micron spaces and ten lo-micron spaces; 

 equal 300 microns. Each division on ocular micrometer equals 6-microns. 2. 

 Ocular micrometer subtending image of whip-worm egg. 9 spaces of ocular mi- 

 crometer cover whip-worm egg. Each space equals 6 microns. Whip-worm egg 

 equals 54 microns. 3. Ocular micrometer with ruling of hsemacytometer. 50 

 spaces of ocular micrometer cover space equal to width of 6 small squares 50X6 = 300 

 microns. Each division of ocular micrometer equals 6 microns. 



Example: With a %-inch objective, the 50 rulings of the ocular micrometer 

 fill in fifteen of the ^ -mm. rulings (loojx) and three of the Hoo-mm. spaces (io/z). 

 Consequently the 50 spaces of the ocular cover 1530 microns (15 X 100 = 1500; 

 3 X 10 = 30). Then if 50 spaces equal 1530 microns, one space would equal 

 30.6 microns. With the J^-inch objective the 50 ocular spaces would cover about 

 three of the J^f o mm. (ioo/u) spaces of the stage micrometer. Then the 50 spaces 

 would equal 300 microns and one space would equal 6 microns. 



The ruling of the slide of a Thomas-Zeiss haemocytometer will answer as well 

 as a stage micrometer. The small squares are %Q mm. square, consequently 



