METHODS OF RESEARCH: PREPARATION OF CULTURE MEDIA 101 



especially for the study of parasites. Before proceeding to a 

 discussion of these cultural substances, the student should read 

 quite carefullythat part of the preceding chapter on Apparatus, 

 and also what he can find on the making of culture media in 

 other text books. 



In the preparation of culture-media one must be governed by 

 the substances and the apparatus at hand. The simplest sub- 

 stances to prepare are cylinders and slices of potato, carrot, 

 and other vegetables, and these are still of great use in the 

 study of diseases of plants, and not to be discarded for purely 

 synthetic media. These vegetable substances may be used 

 either cooked or raw. If cooked, they are best kept in cotton- 

 plugged test tubes in the form of slant cylinders, standing with 

 the bottom immersed in a small quantity of water or free on 

 wet cotton. If raw, they may be cut into the form of cubes or 

 slabs and placed in deep Petri dishes. We will first discuss the 

 proper preparation of such media. A great variety of cooked 

 vegetable substances can be used, both for study of pure sub- 

 cultures of the various micro-organisms, and in default of gelatin 

 or agar for their isolation from the diseased plants. We will, 

 therefore, first consider the proper preparation of these sub- 

 stances. 



Steam-sterilized Solid Vegetable Substances. — Select sound 

 carrot roots, potato tubers, turnips roots, and similar vegetables, 

 wash thoroughly under the tap with hand-rubbing or brush- 

 scrubbing to free from dirt, and with a clean knife pare away 

 the outer surface, being careful to contaminate the inner por- 

 tions as little as possible by contact with the outer surface 

 of the parings or with soiled hands. The remainder may 

 now be thrown into beakers of sterile water and rinsed, after 

 which cylinders may be punched out with a nickel-plated cork 

 borer of the proper size, slanted with a sharp knife and, after 

 a preliminary rinsing, dropped by means of sterile forceps into 

 clean test tubes after which the necessary amount of water 

 should be added and the tubes plugged with clean cotton. The 

 cylinders should be smaller than the bore of the test tube so 

 that there may be room for the water, otherwise they soon dry 

 out and are not then suited for the growth of many organisms. 



