CRYPTOGAMS 261 



223. BACTERIA 



Object. To prove the presence of bacteria in water. 



Apparatus. Test tubes, culture medium, and sterilized cotton. 



Method. Fill two test tubes with the culture medium 

 to about i their depth. Pour into one about 10 cc. of 

 drinking water and close the mouth of the tube with a plug 

 of sterilized cotton. 



Into the second tube, pour the same amount of water 

 which has been boiled. Plug the second tube as before and 

 place both preparations at a temperature of 36 C. 



After several days, examine both tubes, making note of 

 any differences in color, odor, and reaction on litmus. What 

 effect has boiling upon the water used ? 



Suggestion. In like manner, try different samples of 

 water, such as that from wells, cisterns, streams, pools, 

 ditches, etc. 



224. BACTERIA 



Object. To demonstrate the prevalence of bacteria. 



Method. Make several cultures, using such things as 

 tartar from the teeth, scrapings from the finger nails, phlegm, 

 pus, saliva, etc. 



Make cultures, using money, articles of clothing, door 

 knobs, tool handles, and books as sources of bacteria. 



Prepare Petri dish with sterilized culture medium and 

 let a fly walk over the surface and leave it for several days. 

 Touch a lead pencil which has been used to the agar in a 

 Petri dish. What result? 



Make two cultures of any sort of bacteria and add a drop 

 of corrosive sublimate, formalin, carbolic acid, Platt's chlo- 

 rides, or any other disinfectant to one of them. Label the 

 cultures and set them away for observation. Result ? 



