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MICROMETRY AND BLOOD PREPARATIONS 



The ocular micrometer is usually ruled with 50 or 100 lines or spaces, 

 separated by longer lines into groups of 5 and 10. 



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. 



FIG. 50. Micrometry diagrams, i. Ocular micrometer with stage micrometer. 

 50 spaces of ocular micrometer cover two 100 micron spaces and ten 10 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 Whipworm egg. Each space equals 6 microns. Whipworm egg 

 equals 54 microns. 3. Ocular micrometer with ruling of haemacytometer. 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. 



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

 always be adhered to in subsequent measurements. 



Example : With a 2/3-inch objective, the 50 rulings of the ocular micrometer 

 fill in fifteen of the i/io millimeter rulings (ioo/<) and three of the i/ioo millimeter 

 spaces (IQ/X). Consequently the 50 spaces of the ocular cover 1530 microns (15 X 100 

 = 1500; 3X10 = 30). Then if 50 spaces equal 1530 microns, one space would equal 



