NON-REPRODUCIBLE MEDIA 51 



These fungi were found to develop in normal and in some cases 2 A^ 

 and 2.5 A'" sulphuric acid to which 1 gram of peptone and 1 gram of 

 glucose per liter were added. 



Kadisch ^^ studied the influence of the hydrogen-ion concentration 

 upon the growth of various dermatophytes, in the range from pH 

 6.7 to pH 7.9, and found that all of them grew better in slightly 

 alkaline media. The optimum for most species was pH 7.4. Von 

 Mallinckrodt-Haupt -^ observed that two species of dermatophytes 

 when grown on media nearly neutral in reaction made the media 

 progressively more alkaline (up to pH 8), whereas a Penicillium and 

 a pink yeast produced acid. The alkali-preference of the ringworm 

 fungi was offered by Levin and Silvers ^^ as an explanation for the 

 localization of these fungi in the interdigital spaces and the axillae, 

 where the pR of the skin secretion is higher than on other parts of 

 the body surface. 



Nearly all actinomycetes prefer an alkaline medium. Soil actino- 

 mycetes grew in the range pH 5 to 9, with the optimum at pH 7 to 8. 

 Jensen, however, found strains in acid peat soils which grew only in 

 the range pH 2.5 to 5.8 with the optimum at pH 3 to 4. See page 

 362. 



Types of Media. Culture media used in the study of molds may 

 be divided into three groups: 



1. Non-reproducible media, such as pieces or infusions of fruits, 

 vegetables, skin, or hair, which may be valuable for the cultivation 

 of certain species, but which are not reproducible because the sub- 

 strates naturally vary in composition. 



2. Reproducible media of unknown composition. In this group 

 would fall the well-known Sabouraud's medium and its various sub- 

 stitutes. These are media containing complex substances such as 

 peptone whose precise chemical constitution is unknown, but which 

 are manufactured by standardized procedures so that the product 

 from one manufacturer is reasonably constant over a period of time, 

 and the same material is available to all laboratories. 



3. Synthetic media, i.e., media prepared from pure chemicals of 

 known constitution, which can be reproduced precisely in laboratories 

 throughout the world independently of any manufacturer. 



Non-reproducible Media. Media of this class are seldom used ex- 

 cept in infusions or for particular purposes, as the cultivation of 

 species of fungi which will not grow upon the other types of media, 

 or which will produce characteristic fruiting bodies only upon a cer- 

 tain substrate. 



