BACTERIOLOGICAL TECHNIC. 



37 



is, absolutely clean. The following solution will be found useful as a cleans- 

 ing agent for old as well as new glassware: 



Potassium Bichromate, 6 parts. 



Sulphuric Acid, 30 parts. 



Water, 40 parts. 



Of course, the sulphuric acid must be added little by little with constant 

 stirring, in order to avoid excessive heat development. Soak the glassware 



FIG. 12. Wire baskets for holding test-tubes. Cylindrical form and square form. 

 Each basket holds about fifty test-tubes. The wire is galvanized to prevent rusting. The 

 round wire baskets should be used. 



in this solution for some time, several hours or more, and rinse, wash, drain, 

 and wipe thoroughly afterward. The sole object to be attained is cleanliness 

 in the true sense of the word. The glassware must be clean bacteriologically 

 and chemically; that is, it must be free from mi- 

 crobes and chemical substances. 



2. Plugging Containers with Cotton. 



After the thorough cleansing above outlined, 

 the test-tubes and flasks are plugged with a good 

 quality of non-absorbent commercial cotton. The 

 dry cotton plug forms a most efficient germ filter. All 

 microbes are caught and held in the meshes of the 

 cotton, and yet the air is permitted to pass through 

 into the tube or flask. 



Open a roll of cotton, find the free end, and lay it 

 out on the work table. Take the test-tube in the left 

 hand; remove a goodly tuft of cotton with right 

 hand, using thumb and first and second fingers. 

 Place this over the mouth of the tube or flask, and 

 push it down to a distance of 1/2 to 3/4 inch 

 glass rod rounded (by heat) at the ends. The 



Fig. 13. Wire basket 

 filled with test-tubes plug- 

 ged with cotton. A little 

 cotton should be placed 

 in the bottom of the bas- 

 ket to lessen the danger of 

 breaking the test-tubes. 

 (Williams.) 



by means of a solid 

 rod must not be too 



