170 BACTERIOLOGY. 



basis of all bacteriological work. The potato was the first 

 medium employed for isolating- bacteria. In time, other 

 media were introduced, but the fundamental principle, that 

 of physical dilution, is the same, regardless of the medium 

 employed. 



In this, and all subsequent work, successful results and 

 freedom from personal danger depend upon the rigid steril- 

 ization of all articles used. Attention to the smallest de- 

 tail is necessary in order to prevent contaminations. The 

 training, thus acquired, will be invaluable, in time, in the 

 intelligent prevention of disease. The following rule can- 

 not, therefore, be emphasized too strongly: Sterilize all in- 

 struments, wires, etc., immediately before use and immediately 

 after use. Instruments are sterilized immediately before use 

 in order to avoid contaminations; and immediately after use, 

 in order to prevent personal danger. This rule should be 

 rigidly adhered to. Careless manipulations, acquired while 

 engaged in the study of non-pathogenic bacteria, may be 

 unconsciously resorted to when studying disease-producing 

 organisms. A careless student is a source of danger, not only 

 to himself but also to his neighbors. The sterilization of 

 all instruments should be attended to, before they are placed 

 back on the table. 



Certain additional personal precautions should be ob- 

 served, while engaged at work in the laboratory. Pencils, 

 pens, glass rods and labels should never be introduced into 

 the mouth. The tumblers, or glasses in the desk should not 

 be used for drinking purposes. If any material drops on the 

 table or floor, it should at once be rendered harmless by 

 covering it with the mercuric chloride solution. Invariably, 

 at the close of the day's work, the table should be washed 

 with this solution and, at the same time, the hands should 

 be disinfected. 



Laboratory work. Make a dilution culture, as described (on three 

 potatoes), of the Bacillus prodigiosus. 



