2272 



Journal of Applied Microscopy 



It is evident that such a rate as this cannot long be kept up, but theoreti- 

 cally it is possible and practically it is true that a few germs which form a mass 

 so small that it requires the highest powers of the compound microscope to see 

 them can in a few hours, on a good culture medium, as a cooked potato, become 

 numerous enough to form a mass large enough to be readily seen by the naked 

 eye. 



Method of Multiplication. The bacteria reproduce themselves by elongating 

 to what may be considered an abnormal length, then form a partition across 

 their shortest diameter, which divides and thus cuts the organism in two. These 

 new formed individuals soon grow to maturity and then in turn divide into 

 two, as shown in Fig. 9. 



Culture Material. A great many different materials may be used as culture 



media. Most frequently a beef broth is 

 used, either alone or with the addition 

 of certain solidifying substances as gel- 

 atin or agar. Milk is an excellent cul- 

 ture medium, as also are blood serum, 

 egg and cooked potato. 



Potato Cultures. The culture medium 

 easiest prepared for the cultivation and 

 isolation of bacteria is the potato medium. 

 The method of preparing and seeding 

 this medium will now be described. 



Cleansing a)u! Sterilization of Potatoes. 

 Select three potatoes of such size that 

 they will go into the top of a glass 

 tumbler. The skins should be smooth 

 and as free as possible from " eyes " 

 and rotten spots. Wash the potatoes 

 thoroughly, using a brush to remove the dirt, and with a knife remove the "eyes," 

 injuring the skin as little as possible. 



Now place the potatoes in a steamer and cook them about three-quarters of 

 an hour, or until they are done ; or the potatoes may be placed in an oven and 

 baked until done. While the potatoes are cooking the receptacles which are to 

 be used may be prepared. 



Preparation of Receptacles. Six ordinary tea saucers with a like number of 

 glass tumblers are to be washed in boiling water, or better baked in the oven. A 

 circular piece of blotting or filter paper somewhat larger than the top of the 

 tumbler is placed on the saucer and the tumbler inverted over this. If the 

 amount of water which drips from the tumbler is not enough to completely moisten 

 the paper, more should be added. 



Halving the Potatoes. After the potatoes have been allowed to cool some- 

 what in the steamer or oven they are to be halved and placed in the receptacles 

 prepared for them. The hands are washed in hot water and wiped with a clean 

 towel. The blade of a potato or case knife is heated very hot in the flame of a 

 Bunsen burner, of an alcohol lamp, or on the surface of a hot stove. A potato 



Fig. 10. 



-Method of Halving Potatoes (after 

 Crookshank). 



