6 IN TROD UC TION. 



lized magenta. Dissolve in 160 cc. distilled water, to 

 which I cc. of alcohol has been added. 4 



The best commercial glycerine should be used. See 

 that it is colorless and free from sediment. 



A 75 per cent, solution of sulphuric acid should be 

 prepared by mixing three volumes of c. p. sulphuric 

 acid with one volume of distilled water, being very 

 careful to pour the acid slowly into the water while 

 stirring it. 



The potassic chlorate solution may be prepared as fol- 

 lows : Dissolve 2 gm. potassic chlorate in 5 cc. nitric 

 acid. 



III. USE OF THE MICROSCOPE AND LENS. 



The prime requisite in the use of any optical instru- 

 ment is cleanliness: dirty lenses frequently defeat the 

 very object of their use, namely, clearer vision. Before 

 beginning to work with either the simple or compound 

 microscope, see that the lenses are perfectly clean. 

 When a lens needs cleaning, take a camel's-hair brush 

 and brush away all particles of dust. Then wipe gently 

 with a piece of soft unstarched linen or cotton an old 

 handkerchief is the best breathing upon the surface 

 slightly if necessary to remove the dirt. Too great care 

 can not be taken to avoid scratching the polished surface 

 of the lens ; hence the least possible effective pressure 

 should be used when wiping it. If properly handled 

 after they have once been cleaned, lenses will seldom 

 need any thing but brushing. One should avoid with 

 the greatest care touching the surface of a lens with 



4 Huxley and Martin, Biology, p. 269. 



