NUTRIENT MEDIA 19 



living structures. Finally a certain amount of moisture 

 is absolutely necessary." (Besson.) 



A food prepared for the growth of microorganisms is 

 given the general term nutrient medium. A large number of 

 microorganisms will grow readily in or upon easily available 

 nutrient media, as milk, bouillon, etc. Some microorgan- 

 isms have widely differing food requirements and need for 

 growth nutrient media differing widely in their composition. 



However, there are a few general rules that must be 

 applied in the preparation of all nutrient media for the use 

 of microorganisms. These are briefly, that: Every culture 

 medium must 1. Contain substances necessary for giowth. 

 2. Be of suitable reaction. 3. Be contained in vessels 

 which afford protection from contamination from without. 



Classification of Nutrient Media. Culture media may 

 be classified as: 



I. Natural Media as occurring in nature, e.g., milk, 

 potato and other vegetables, meat and meat products, blood 

 and blood serum, egg, soil, etc. 



II. Prepared media, i.e., made in the laboratory. These 

 are: 



(a) Of unknown chemical composition; e.g., nutrient 

 agar, gelatin, etc. 



(6) Synthetic; i.e., chemical composition known, e.g., 

 Giltay solution for denitrifying organisms. 



Or as: 



I. Liquid Media. These include: 



A. Media made from animal tissue and fluids, e.g., 

 nutrient broth, serum broth, carbohydrate broths, milk, 

 blood, nitrate peptone solution, Dunham's solution. 



B. Media made from vegetable tissue. Among these are: 

 Malt extract (germinated barley), beer wort, yeast extract, 

 hay infusion, natural fruit juices, wines (fermented fruit 

 juices). 



C. Synthetic media. 



II. Solid Media. These mav be classified as: 



