25 MICROSCOPE AND ACCESSORIES. 



Put a 2 mm. (tVth in.) homogeneous immersion objective in posi- 

 tion, employ an Abbe illuminator. 



§ 66. Refraction Images. — Use some histological specimen like a 

 muscular fiber as object, make the diaphragm opening only slightly 

 larger than the front-lens, add a drop of the homogeneous immersion 

 liquid and focus as directed in §§ 64 and 67. The object will be 

 clearly seen in all its details by the unequal refraction of the light 

 traversing it. The difference in color between it and the surrounding 

 medium will also increase the sharpness of the outline. If an air bub- 

 ble preparation (§ 52) were used, one would get pure, refraction 

 images. 



§ 67. For Color Images. — Use some stained microbes, as Bacillus 

 tuberculosis for object. Put a drop of the immersion liquid on the cov- 

 er-glass or the front-lens of the homogeneous objective. Remove 

 the diaphragms from the illuminator or use a very large opening. 

 Focus the objective down so that the immersion fluid is in contact with 

 both the front-lens and the cover-glass, then with the fine adjustment 

 get the microbes in focus. They will stand out as colored rods on a 

 bright field. 



§ 68. Shading the Object. — To get the clearest image of an object 

 no light should reach the eye except from the object. A handkerchief 

 or a dark cloth wound around the objective will serve the purpose. 

 Often the proper effect may be obtained by simply shading the top of 

 the stage with the hand or with a piece of bristol board. Unless one 

 has a very favorable light the shading of the object is of the greatest 

 advantage, especially with homogeneous immersion objectives. 



§ 69. Cleaning Homogeneous Objectives. — After one is through 

 with a homogeneous objective, it should be carefully cleaned as follows : 

 Wipe off the homogeneous liquid with a piece of the Japanese paper 

 (§ 72), then if the fluid is cedar oil, wet one corner of a fresh piece in 

 benzin and wipe the front-lens with it. Immediately afterward wipe 

 with a dry part of the paper. The cover-glass of the preparation can 

 be cleaned in the same way. If the homogeneous liquid is a glycerin 

 mixture proceed as above, but use water instead of benzin to remove 

 the last traces of glycerin. 



CARE OF THE MICROSCOPE. 



§ 70. The microscope should be handled carefully, and kept perfectly 

 clean. The oculars and objectives should never be allowed to fall. 



When not in use keep it in a place as free as possible from dust. 



All parts of the microscope should be kept free from liquids, especially 

 from acids, alkalies, alcohol, benzin, turpentine and chloroform. 



§ 71. Care of the Mechanical Parts. — To clean the mechanical 



