38 ELEMENTARY PHYSIOLOGY. [IL 



same positions as before, make a drawing of 

 the micrometer lines over the previously 

 made drawing of the corpuscles; then, the 

 real distance between the micrometer lines 

 being known, the diameters of the corpuscles 

 can be at once read off; thus if the micro- 

 meter lines are -j^ mm. apart and in the 

 drawing a corpuscle exactly occupies one 

 division its diameter in that direction is 

 evidently -3-5^ Tum. 



The drawing of the micrometer lines may be 

 kept as a scale, and any object drawn under 

 the same magnifying power and with the 

 pad and microscope in the same relative 

 positions may be directly measured by it. 



b. Substitute for the ordinary eye-piece of the 

 microscope one which has a ledge for sup- 

 porting an ocular micrometer \ the values of 

 which have been determined, the size of the 

 corpuscle can then be at once read off. 

 4. Mount another small drop of blood, place a 

 small drop of "1 p.c. acetic acid on the glass 

 slide so that it just touches the edge of the 

 cover-slip; place a piece of blotting-paper on 

 the opposite side just touching the fluid at the 

 edge of the cover-slip, the acetic acid will then 

 run under the cover-slip and mix with the blood. 

 Note the changes which take place. 



a. In the colourless corpuscle, the cell sub- 

 stance becomes more transparent but shews 



' Cp. Appendix. 



