XXII. 

 THE BACTERIA. 



A. The Harmless or Non-Pathogenic Bacteria. 



Materials. Nutrient gelatin made of 500 grms. of lean beef, 

 finely minced, 1 litre of water, 100 grms. of gold-label gelatin, 10 

 grms. of peptone, 5 grms. of salt, and sodium carbonate. One egg. 



Apparatus. Steam sterilizer, or kettle for steaming. Hot-air 

 sterilizer, or oven for sterilizing with gas stove. Double boiler. 

 Stirring rod. Funnel. Filter-paper. Ring-stand. Bunsen burner. 

 Litmus paper. Cotton-batting. Two glass flasks holding 500 c.c. 

 each. 



To make the nutrient gelatin, mix the beef with the 

 water and allow it to stand about twelve hours. Filter 

 through "cheese-cloth," and to the nitrate or meat-water 

 add the gelatin, peptone, and water. Mix thoroughly in 

 the double boiler and heat for about half an hour. Neu- 

 tralize by adding sodium carbonate, till red litmus paper 

 just turns blue. Boil for about an hour, add an egg to 

 clarify and settle the albuminous matter, and boil a few 

 minutes longer. Filter while hot through filter-paper 

 into sterilized flasks and plug with cotton. Care should 

 be taken to keep the unfiltered gelatin hot, and to wet the 

 filter-paper with hot water before beginning to filter. 

 Sterilize the gelatin in a steam generator twenty-five 

 minutes a day for three days in succession. If the gela- 

 tin is found to be acid at the beginning of filtration, it 



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