APPENDIX. — GENERAL DIRECTIONS. 219 



seing fine details of structure will depend upon the care exercised in this 

 respect. 



5. Bear in mind that many of the reagents used are corrosive and hence 

 should not be brought into contact with the microscope. All the acids and 

 iodine reagents will act upon brass-work, potassium hydrate will corrode glass, 

 and alcohol will remove the lacquering from the stand. 



6. All objects examined in liquids should be covered, not only to obviate 

 the danger of injuring the objective, but to avoid the inevitable distortion of 

 the image which a curved or uneven liquid surface produces. 



7. Let cleanliness and care characterize all your work in the microscopical 

 laboratory. Keep all your apparatus, *lides, cover-glasses, etc., scrupulously 

 clean. Do not touch the glasses of the objectives or eye-pieces with your 

 fingers, for that would be to soil them and impair their optical performance. 

 Whenever they need cleansing, breathe upon the glasses and wipe them either 

 with a p'ece of perfectly clean and soft linen cloth, or with a piece of the thin, 

 soft paper that is sold at dental supply-stores under the name of Japanese filter 

 paper. A convenient way is to keep always at hand, in a place secure from 

 dust, a quantity of this paper cut into suitable sizes. It is useful, also, for 

 cleaning cover glasses, slides, etc. If a fresh piece is used each time for clean- 

 ing an objective, there will be little danger of marring the polish of the front 

 lens. 



Keep the bottles containing reagents, staining fluids, etc., stopped when 

 not in use, so as to exclude dust and prevent evaporation ; and take especial 

 care in using them not to introduce impurities into them. 



8. In cutting sections, the razor or section-knife should always be very 

 sharp, and for most purposes sections should be cut quite thin. Steadiness in 

 cutting is secured by resting the wrists against the body. The knife should be 

 given an oblique or sliding motion when drawn through the object. Quite 

 hard tissues may be successfully cut if the sections are cut quite thin, but if the 

 edge of the knife is allowed to run too deep, it is liable to be notched. Portions 

 of thin structures like leaves, petals, etc., may readily be sectioned by placing 

 them between pieces of Elder or Sunflower pith. Always clean the knife after 

 cutting with it, and do not allow fragments of tissue to dry upon it. Sections 

 of fresh tissues, or of those that have been preserved in any of the preservative 

 fluids, should immediately be placed in liquid after cutting, to prevent air from 

 getting into the cells. 



9. In all your work with the microscope, proceed understandingly. En- 

 deavor to know the reason for every test you are called upon to apply, and be 

 careful in interpreting the results of each test. Do not rest satisfied until you 

 thoroughly understand every tissue and structure given you for study. 



10. It is excellent practice for the student to keep an accurate record in 

 writing, and by means of drawings, of all the facts observed and the work done 

 by him in the microscopical laboratory. 



