CULTURE MEDIA 71 



it while the meat is being digested. In this way the sugar is 

 gotten rid of, and the preparation of the medium goes on from 

 this point as in the case of ordinary bouillon. 



Dunham's Solution. Dunham's solution is used at times 

 for the study of bacteria. It simply consists of a i per cent 

 peptone solution. 



Milk. The milk of cocoanuts has been used in special 

 instances, but cow's milk is very frequently used for growing 

 bacteria. Fresh milk should be secured and the fat separated, 

 preferably by centrifugalization. Milk is sometimes quite 

 difficult to sterilize on account of the very resistant spores 

 which it may contain, and steaming on four or five consecutive 

 days may be necessary. Litmus is frequently added to milk, 

 which increases the usefulness of this very useful medium. 



Among other liquid media used are whey, urine, and beer 

 wort. The latter is used almost exclusively for the growth of 

 yeast. 



Solid Media 



Potatoes. Potatoes were first used by Schroeder. He 

 boiled them with their jackets on and then cut them in two 

 with a sterile knife, placed them in a covered dish, and grew 

 bacteria on the cut surface. Esmarch later used slices of 

 potatoes in special glass dishes which he had made ; but at the 

 present time they are used almost entirely in test tubes and 

 Petri dishes. Cylinders of the potato, with a sloping front 

 surface, are put in test tubes which are sterilized and used as 

 other test tube media. It is desirable that the color 



