EXAMINATION AND STAINING OF BACTERIA. 41 



What is the effect of moisture on bacterial life ? Of desiccation ? 

 What pabulum is necessary for the life of bacteria ? 



How do you explain the life of bacteria in saline solution and in media 

 with no appreciable amount of organic matter? 

 What is meant by culture-soils or media ? 

 What other conditions influence bacterial growth ? 



What is the effect of sun-light on bacteria ? Of electric currents ? X-rays ? 

 Of compressed air? 



What are the manifold functions of bacteria ? Enumerate and explain 

 the same. 



What is the chemical difference between a ptomaine and a toxalbumin? 

 What are zymogenic ? Chromogenic? Photogenic? Pathogenic bacteria? 



CHAPTER II. 

 THE EXAMINATION AND THE STAINING OF BACTERIA. 



THE EXAMINATION OF BACTERIA. 



FOE the purpose of examining bacteria the highest power 

 of the microscope is necessary, although many are seen with an 

 ordinary dry ^ or ^ objective. Ordinarily, however, the ^ 

 oil-immersion objective is indispensable for the proper study 

 of microorganisms. 



Bacteria are examined either alive and in their natural con- 

 dition, or dried on microscope slides or cover-glasses as a 

 thin film, and stained. 



1. For the purpose of examining bacteria in their natural 

 condition, it is only necessary, when the bacteria are in liquid 

 medium, to put a droplet of the liquid on a slide, cover lightly 

 with a thin cover-glass, put upon the stage of the microscope, 

 and bring into focus the y 1 ^ inch oil-immersion objective, 

 being careful to close almost completely the iris diaphragm 

 underneath the substage condenser. 



When the bacteria are in solid medium, a minute particle of 

 the culture is taken up on a sterilized platinum needle and 

 stirred up in a small drop of sterilized water on a slide, and a 

 cover-glass applied as above. 



In these ways the form, shape, mode of grouping, and motility 



