2 7 



MICROSCOPE AND ACCESSORIES. 



Canada Balsam, damar, paraffin, or any oily substance, may be re- 

 moved with a cloth or paper wet with chloroform, turpentine or benzin. 

 The application of these liquids and their removal with a soft, dry cloth 

 or paper should be as rapid as possible, so that none of the liquid will 

 have time to soften the setting of the lenses. 



Shellac Cement may be removed by the paper or a cloth moistened in 

 95 per cent, alcohol. 



Brunswick Black, Gold Size, and all other substances soluble in chlo- 

 roform, etc., may be removed as directed for balsam and damar. 



In general, use a solvent of the substance on the glass and wipe it off 

 quickly with a fresh piece of the Japanese paper. 



It frequently happens that the upper surface of the back combination 

 of the objective becomes dusty. This may be removed in part by a 

 brush, but more satisfactorily by using a piece of the soft paper loosely 

 twisted. When most of the dust is removed some of the paper may be 

 put over the end of a pine stick (like a match stick) and the glass sur- 

 face carefully wiped. 



CARE OF THE EYES. 



§ 73. Keep both eyes open, using the eye-screen if necessary (Fig. 

 18, and PI. II, Fig. 16) ; and divide the labor between the two eyes, i. 

 e. t use one eye for observing the image awhile and then the other. In 

 the beginning it is not advisable to look into the microscope continu- 

 ously for more than half an hour at 

 a time. One never should work with 

 the microscope after the eyes feel fa- 

 tigued. After one becomes accus- 

 tomed to microscopic observation he 

 can work for several hours with the 

 microscope without fatiguing the eyes 

 the eyes become inured to labor like the other organs of the body by 

 judicious exercise. It is also due to the fact that but very slight accom- 

 modation is required of the eyes, the eyes remaining nearly in a condi- 

 tion of rest as for distant objects. The fatigue incident upon using the 

 microscope at first is due partly at least to the constant effort to accom- 

 modate the eye for a near object. With a microscope of the best quali- 

 ty, and suitable light — that is light which is steady and not so bright as 

 to dazzle the eyes nor so dim as to strain them in determining details — 

 microscopic work should improve rather than injure the sight. 



A LABORATORY COMPOUND MICROSCOPE. 



\ 74. For the purpose of modern histological investigation and of advanced mi- 

 croscopical work in general, a microscope should have something like the follow- 

 ing character : Its optical outfit should comprise, (a) dry objectives of 50 mm. (2 



Fig. 18. — Ward's Eye-Shade. 



This is due to the fact that 



