3o8 BACTERIA, YEASTS, AND MOLDS 



Microscopic Study of Bacteria 



It is rarely feasible to carry on any extended microscopic study of 

 bacteria with ordinary classes. The organisms are so minute that 

 they require very high powers and expensive microscopes, and are so 

 simple that the scholar can learn very little by their study. A brief 

 examination of a few bacteria may, however, be useful. If desired it 

 can be done as follows. 



48. Study of Living Bacteria. Obtain a bit of decaying meat, 

 decaying egg, or some other proteid material, and place a minute 

 drop of it upon a slide in a drop of water ; cover with a cover glass 

 and study with the highest objective obtainable. A ■j'5-inch objective 

 is required to study them, but a -l-inch will usually be sufiScient 

 to show the bacteria as minute specks, many of which will commonly 

 be seen swimming rapidly under the field of the microscope. If 

 decaying material from different sources is studied, there will usually 

 be found several kinds of bacteria, as indicated by the different sizes 

 and shapes. 



49. Staining Bacteria. To make a more careful study of these 

 organisms, they must be stained in order that they may be more 

 clearly visible. Staining fluids may be bought or a convenient one 

 be prepared as follows: 



ZiehVs Carbol-Fuchsin 



Saturated alcoholic solution of fuchsin 5 cc. 



Five per cent, solution of carbolic acid 45 cc. 



To stain bacteria place a very small drop of some decaying mixture 

 upon a cover glass in a drop of clear water. Spread it over the cover 

 glass in as thin a layer as possible, and then allow it to dry in the air. 

 After drying take the cover glass in a pair of forceps and pass it rap- 

 idly through a gas flame three times. This is Xafix the bacteria upon 

 the slide. Place a few drops of the staining fluid upon the bacteria 

 on the cover glass and allow the stain to remain for five minutes. 

 Then wash thoroughly in a stream of running water and place the 

 cover glass upon a slide in a drop of water, bacteria side down. 

 Study with the highest-power objective. The bacteria will be found 



