94 LABORATORY GUIDE IN BACTERIOLOGY 



turbidity, and by preparing stains with gentian violet 

 from small amounts of the material in the culture 

 media. 



SECTION 6 



INFLUENCE OF DISINFECTANTS, LIGHT, AND HEAT 

 ON THE GROWTH OF MICRO-ORGANISMS 



For precise methods see: 



Anderson and McClintic, Hyg. Lab. Bull. 82, 1912. 

 Amer. Jour, of Public Health, October, 1912. 

 Rideal and Walker, ibid., June, 1913. 



North Dakota Agricidtural College, Special Bulletin, July, 

 August, 1913. 



EXERCISE I 



1. Prepare fifty-seven Hill's test rods. These are 

 prepared in the following manner: Glass rods about 

 two inches lohger than ordinary culture tubes are 

 marked with hydrofluoric acid or a glass cutter (dia- 

 mond or file) by a circle one inch from the end. A 

 wad of cotton is then wrapped around the middle of 

 the rod, and inserted in a culture tube. The rod is 

 then pushed down until it nearly reaches the bottom. 

 That part of the rod which is free at the upper end is 

 used for labeling. The whole apparatus is sterilized 

 in the dry-air oven. 



2. Fill two wide-mouthed flasks, one with 100 c.c. 

 of a s per cent solution of carboUc acid, the other with 

 100 c.c. of a I per cent solution. 



3. Fill two similar flasks, one with 100 c.c. of a solu- 

 tion of mercuric chlorid i : 1,000, the other with a solu- 

 tion of 1 : 10,000. 



