PART II. 



LESSON I. 



MILK, GRANULES, FIBRES, AND VEGETABLE 

 ORGANISMS. 



1. Examine the Microscope, the objectives, and the eye-pieces. 



(a.) Select the objective and ocular required. For a high power 

 (H), if a Zeiss' microscope be used, select the objective D and the 

 ocular 2 ; if Hartnack's, the objective No. 7 and the eye-piece III. 

 See that the lenses are clean. Place the ocular in the tube, and 

 screw the H lens to the lower end of the tube, and leave it half an 

 inch above the level of the stage. For a low power (L) use No. 2 

 ocular of Zeiss or III. of Hartnack, and objective A or No. 3 

 respectively. In using a low power, the lens must be i^ inches 

 above the stage to begin with. 



(/;.) With the microscope in front of you, with high-power lens 

 on it, arrange the concave side of the mirror under the stage so as 

 to reflect a beam of light up the tube of the microscope into the eye, 

 looking in at the ocular. Turn the sub-stage diaphragm until a 

 small aperture in it is under the aperture in the centre of the stage. 

 If any specks are visible on looking through the microscope, rotate 

 the ocular ; if they move, of course they are on the ocular itself. 

 Clean the outer surfaces of the lenses of the ocular with a piece of 

 clean wash-leather, which should be kept tied to the microscope and 

 used for no other purpose than cleaning the lenses. Replace the 

 ocular, and if specks are still present and move when the ocular is 

 moved, they must be on the inner surface of the eye-glass or field- 

 glass of the latter. This is easily determined by rotating the eye- 

 glass of the ocular alone, while looking through the microscope, and 

 observing if the specks do or do not move with it. Clean the inner 

 surfaces of these lenses. A general dimness indicates that the objec- 

 tive itself is dirty. The light used should not be direct sunlight, 

 but preferably light reflected from a white cloud. 



10 G 



