76 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



nitrogen compounds in the form of amino acids, peptids, 

 peptones, and in a few instances apparently even more 

 complex organic compounds. 



Media are sometimes divided into synthetic and nonsyn- 

 thetic. A synthetic medium is one in which the exact 

 chemical composition of each of the components is known. 

 A nonsynthetic medium is one in which the exact chemical 

 composition is not fully understood. Some kinds of bac- 

 teria can be studied best by the use of the simple synthetic 

 media, but suitable ingredients for such media are not 

 readily available for many other kinds of bacteria. 



Synthetic media usually contain as a basis an aqueous 

 solution of certain salts, among them potassium phosphate 

 and sodium chloride. One of the most commonly used is 

 Uschinsky 's solution : 



Water, distilled 1000 c.c. 



Asparagin 4 grams 



Ammonium lactate 6 grama 



KjHPO, 2 grams 



NaCl 5 grams 



Media of this type have proved very useful in studying the 

 products of fermentation of microorganisms. 



Were it possible to secure pure amino acids and peptids 

 in commercial quantities, suitable synthetic media for many 

 of the pathogenic bacteria could be devised which would be 

 of real value in their study and differentiation. 



The basis for most laboratory media is nutrient broth or 

 bouillon. It contains either meat infusion or meat extract, 

 peptone, usually salt, and water. Meat infusion is pre- 

 pared by soaking 500 grams of lean minced beef in water 

 in the ice chest for twenty-four hours, filtering the liquid 

 through cheesecloth by means of a meat press, and making 

 up the filtrate to one liter. Meat extract broth is prepared 

 ty using (in place of the meat infusion) about three grams 

 of commercial beef extract to a liter of water. 



Many makes of peptone are upon the market. Peptone 



