CHAPTER VIII. 



THE MICROSCOPICAL EXAMINATION OF CULTURES 

 OF MICRO-ORGANISMS. 



Introduction. 



Section I. The preparation of slides and cover-glasses, p. 130. 

 Section II. The examination of unstained preparations, p. 131. 

 Section III. The examination of stained preparations, p. 135. 



1. Staining solutions, p. 137. 2. Simple staining, p. 140. 3. Gram's stain, p. 142. 

 4. Claudius' method, p. 144. 



CULTURES should be examined microscopically in two ways. 



(a) An unstained preparation of the living organisms should first be 

 examined. By this means not only can the shape of the organisms be 

 determined but also whether they are motile or not, and if motile the nature 

 and rapidity of the movements. 



(6) Secondly, the morphological study of an organism must be completed 

 by the examination of stained preparations, which will allow a more detailed 

 study of its structure with the higher powers of the microscope. 



For the preparation of objects for the microscope a supply of clean slides 

 and cover-glasses is essential, and the methods of preparing these may first 

 be described. 



SECTION I. THE PREPARATION OF COVER-GLASSES AND SLIDES. 



The essential qualities of cover-glasses and slides have already been men- 

 tioned (p. 119). Before being used they must be carefully cleaned. 



1. Cleaning of cover-glasses and slides. 



A. New cover-glasses are more or less greasy and cannot be moistened 

 with water. Before using them therefore wash them in 95 per cent, alcohol, 

 and wipe with a piece of soft smooth-surfaced cloth ; then to get them 

 perfectly clean they must be passed several times through the heating flame 

 of a Bunsen burner. 



In wiping a cover-glass never hold it in both hands because it will certainly 

 be broken, but hold it between the folds of the cloth with the thumb and 

 first finger of the right hand, and rub it gently. 



It is convenient to have a wide-mouthed ground-glass stoppered pot on 

 the bench containing 95 per cent, alcohol in which to keep a stock of cover- 

 glasses, so that they can be taken out and dried as wanted. 



