GENERAL BIOLOGY 



A. PREPARATION OF CULTURES FOR 



FUTURE STUDY 



1. BACTERIA OF HAY INFUSION. 



Fill three test-tubes l / 2 full of a fresh infusion of hay: (i) care- 

 fully close one tube with cotton wool and boil a few minutes; (2) 

 do the same with a second tube and then boil it again after 24 hours 

 and repeat the boiling for several days if convenient; (3) leave a 

 third tube open and do not boil it; set all three in a warm place 

 where they can be observed from time to time. 



2. BACTERIA OF THE AIR. 



Clean a smooth potato with a stiff brush and water, removing 

 with a knife all injured portions as well as the buds ("eyes"). Ster- 

 ilize the potato in boiling water for thirty minutes, then cut 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. 



3. BACTERIA OF HYDRANT WATER. 



Take a sterilized gelatin culture plate in a Petrie dish, 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. 



4. 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. 



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