70 LABORATORY BACTERIOLOGY 



EXERCISE XXX 



PYOGENIC BACTERIA {Continued) 



110. Work for this Exercise. — Examine and carefully de- 

 scribe the cultures made in Exercise XXIX. Note especially 

 the growth on the agar, gelatin, potato, and in the tubes of the 

 bouillon containing the sugars. In describing the color, use 

 color charts which are in the laboratory. 



Examine microscopically in (i) hanging-drop and (2) stained 

 (alkaline methylene-blue) cover-glass preparations the bacteria 

 from each of the bouillon and agar cultures. 



Measure a few of the bacteria in the stained preparations 

 from the agar cultures, and make a drawing of them, magnified 

 1000 diameters. 



Inoculate for Exercise XXXI. a tube of each medium in 

 Groups A and B from a culture (furnished) of Pseudo- 

 monas (Bacillus) pyocyaneus. 



For suggestions in studying cultures and microscopic prep- 

 arations of bacteria, see Exercises VI. and XII. 



111. Making Drawings of Bacteria with a Definite Magnifica- 

 tion. — In measuring the bacteria we obtain the dimensions in 

 microns or in units of i/iooo of a millimetre. In making a 

 drawing, therefore, showing them magnified 1000 diameters, 

 it is simply necessary to represent each micron by i milli- 

 metre. Thus,, if the organism is 2.5 \i. in length and i /* broad, 

 the drawing should be 2.5 mm. long and i mm. broad. If the 

 drawing is to represent the organism magnified 500 diameters, 

 then each micron should be represented by 0.5 mm. For this 

 purpose a metric rule and a pair of dividers are necessary. 



