A BACTERIOLOGICAL METHOD USEFUL FOR THE STUDY 
OF OTHER MICRO-ORGANISMS 
Freda M. Bachmann 
We have been using in some studies of bacteria for the past two 
years a method which appears to be equally valuable for the study of 
other micro-organisms. The bacteria are grown in a thin film of 
medium upon a microscopic slide and later stained. It was devised by 
Frost^ in his studies on the bacteriology of milk in order to obtain a 
more rapid method of counting living bacteria in milk than the ordinary 
or standard plate method. It is invaluable not only to determine 
quickly the number of organisms in any richly seeded material, but 
also for a study of the morphology of the single cells or of the colonies. 
Very beautiful preparations may be obtained which show the relation 
of the cells to each other as well as the cytology of the individual cells. 
Recently I have applied this method slightly modified to the study of 
the yeast cell with very gratifying results. 
Thaxter's potato hard agar, which consists of potato broth with 
3 percent agar and 2 percent dextrose, is a favorable medium for the 
growth of yeasts. It is important that the medium be very clear. 
This is accomplished by the addition of egg albumen, followed by 
boiling and filtering according to the usual methods of procedure in the 
making of media. In this way it is possible to obtain a clear amber 
liquid which becomes only slightly less clear as it solidifies. This is 
introduced in approximately 5 cc. amounts in test tubes and 
sterilized. 
When the plates are made, the slides are first thoroughly cleaned to 
free them from grease or other adhering material, then sterilized in 
the flame from a Bunsen burner and then placed on a warm stage. 
The temperature of the slides should be somewhat above the solidifying 
point of the medium used. The agar is liquefied and cooled to not lower 
than 45 °, then inoculated with about i/io cc. of a rather heavy suspen- 
sion of yeast cells in water. These are evenly distributed in the medium 
1 Frost, W. D. A Rapid Method of Counting Living Bacteria in Milk and 
Other Richly Seeded Materials. Jour. Amer. Med. Assoc. 46: 889-890. 1916. 
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