potato in boiling water for thirty minutes, then cut it in slices by 

 means of a knife sterilized in a Bunsen flame. Place the slices of 

 the potato on a sterilized glass plate and leave the clean cut surface 

 exposed to the air in the room for one hour. Cover with a sterilized 

 bell jar under which some distilled water is placed to maintain a 

 moist atmosphere and set aside for several days. If any organisms 

 develop on the potato they must have come from the air of the 

 room. Observe on the potato variously colored spots or "colonies". 

 Are all of these colonies bacteria? Are all the organisms in a colony 

 alike? \Yhat is the significance of this fact? 



C. BACTERIA OF HYDRAXT WATER. 



Take a sterilized gelatin culture plate in a Petrie dish (each locker 

 is supplied with one) open the dish and quickly allow a few drops 

 of hydrant water to run across the gelatin. Close the dish at once 

 and set it aside for several days. If bacteria were present in the 

 water one or more colonies of them will be found along the path of 

 the drop. Study these colonies as in the preceding experiments. 



D. BACTERIA OF MILK. 



Dilute i cc. of milk with 100 cc. of sterilized water. Add i cc. of 

 this dilution to a Petrie dish of "litmus agar", cover and place in 

 the incubator for 36 hours. Then by means of a "counting plate" de- 

 termine the approximate number of colonies present in the agar, and 

 calculate the number of bacteria present in i cc. of undiluted milk. 

 Colonies which have the form of minute footballs belong to the 

 group of "colon bacilli" and come from the intestinal tract of some 

 mammal. AYhat does the changed color of the litmus agar indicate? 



E. BACTERIA FROM THE MOUTH. 



Take some scrapings from the teeth, dilute with water, mount 

 and study the various forms under a high power. How many kinds 

 of bacteria can you find ? 



F. MOTILE STAGES. 



Study bacteria from various media, viz. : Pasteur's Solution, Beef 

 Tea, Infusions of Hay and Peas, Potato and Gelatin Cultures, Sew- 

 age, etc., and observe and draw the following forms: 



1. Micrococcus; rounded forms occurring singly or in bead-like 

 TOWS ; without flagella. 



2. Bacterium; short and thick rod-like forms. 



3. Bacillus; long thread-like forms. 



