IO 



APPARATUS 



culturing slow growing organisms, as tubercle bacilli, or certain pathogenic protozoa 

 it is necessary to have plugs so prepared as to prevent drying out of the medium in the 

 tube. The simplest way of accomplishing this is to melt some paraffin in a pan, then 

 removing the cotton plug with the fingers to dip the end entering the tube into the 

 melted paraffin and then push the surface so prepared into the tube. Plasticine, 

 sealing wax or paraffin may be used to seal over the tops of such test-tubes. 



Cleaning Fluid. The cleaning fluid commonly used in laboratories consists of i 

 part each of potassium bichromate and commercial sulphuric acid with 10 parts of 

 water. This is an excellent mixture for cleaning old slides, etc., especially when 

 grease or balsam is to be gotten rid of. It is very corrosive, however. 



FIG. 2. i, Inoculation of tubes; 2, plugging of tubes; 3, filling tubes; 4, Smith's 

 fermentation tube; 5, Durham's fermentation tube. 



In cleaning glassware for such tests as the colloidal-gold one it is essential that we 

 use such a cleaning fluid. An efficient and less corrosive method for cleansing slides 

 and cover-glasses is to leave them over night in an acetic acid alcohol mixture (two 

 parts of glacial acetic acid to 100 parts of alcohol). After drying and polishing out 

 of this mixture, it is well to pass the slides and cover-glasses through the flame of 

 a Bunsen burner or alcohol lamp to remove every vestige of grease. Ordinarily, 

 rubbing between the thumb and forefinger with soap and water, then drying with 

 an old piece of linen, and finally flaming will yield a perfect surface for making a 

 bacterial preparation. 



