SYNTHETIC MEDIA 55 



phytes because it permits comparison with the excellent photographs 

 Sabouraud used to illustrate his taxonomic studies. The ingredients 

 used by Sabouraud are no longer generally available and so many 

 substitute formulas have been proposed that the name Sabouraud 's 

 medium as commonly used has no precise meaning. The substitu- 

 tion of 1 per cent Neopeptone (Difco) and 2 per cent c.p. glucose 

 with 2 per cent agar and adjustment of pH 5.6 gives a medium which 

 produces very nearly the same type of colony as the original formula 

 and makes use of materials readily available and reasonably con- 

 stant in composition. This medium is referred to in this book as 

 Sabouraud or American Sabouraud agar. For most purposes the pH 

 of the medium need not be adjusted. 



It would of course be highly desirable to obtain a medium of 

 known chemical composition which could be produced in constant 

 form independently of commercial preparations. Unfortunately no 

 medium yet devised will yield a characteristic growth of all of the 

 fungi, especially not of the dermatophytes. Williams ^® found that 

 asparagine was not a satisfactory substitute for peptone. 



Synthetic Media. Synthetic media are most widely used in bio- 

 chemical studies, since a known substrate is essential in order to study 

 the products of metabolism. With a basic medium of precisely 

 known concentration, one may vary the constituents one by one and 

 so determine the influence of each upon growth, enzyme action, and 

 the like. This aspect of the study of fungi has been extensively re- 

 viewed by Steinberg.^^ The first noteworthy studies of this sort 

 were made by Raulin who developed a formula for the growth of 

 Aspergillus niger containing eleven ingredients, all of known chem- 

 ical composition. Such a medium seems unnecessarily complicated, 

 but has served as the starting point for numerous studies, especially 

 of the effects of small quantities of the metals. Raulin's medium is 

 strongly acid ipH 2.9), and for many species the formula will need 

 modification to provide a more favorable reaction. 



Synthetic media are further used, where possible, as a standard 

 substrate upon which to observe colony form and especially pigment 

 production. Such a medium which has been widely used is Czapek's 

 medium as modified by Dox and by Thom: 



Sucrose 30.0 grams 



Sodium nitrate 2.0 grams 



Dipotassium phosphate 1.0 gram 



Magnesium sulphate (crystals) 0.5 gram 



Potassium chloride 0.5 gram 



Ferrous sulphate 0.01 gram 



Water 1 liter 



