250 An Introduction to Medical Mijcology 



as differential as Sabouraud's test medium, internationally mailable and 

 comprised of ingredients which will not vary from year to year. The work of 

 Williams and Southworth indicates that such a standard medium may soon 

 be in common use. For the present, the mediums listed in the following 

 pages are recommended for routine use. 



It should be emphasized that only certain sugars are suitable for inclu- 

 sion in the formulas of mediums. Development of color in a colony or in 

 the adjacent medium may be an important feature of the fungus. We have 

 found that the carbohydrate component of the medium is the fraction 

 used by the fungus for this purpose; most monosaccharides can be utilized, 

 but disaccharides, such as maltose and lactose, and other complex sugars 

 cannot be used by fungi to form pigment. 



Stock cultures may be kept on an ordinary medium until moderate 

 growth has taken place and may then be stored in the refrigerator. To pre- 

 vent contamination in handling and to lessen the drying of the agar, the 

 top of the tube should be covered with cellophane kept on with a rubber 

 band. We have found cellophane better than tin foil or wax paper, as it is 

 transparent and labels or crayon marks may be seen through it without 

 its being removed. In addition, cellophane is punctured less easily than tin 

 foil when one is handling the tubes. Under the conditions described, col- 

 onies may be kept for three to six months. 



The addition of yeast extract powder to standard medium enhances the 

 features of the fungus, such as the formation of spores, characteristic color 

 and contour. It seems to reduce the tendency for the organism to become 

 pleomorphic. 



1. FORMULAS 



The artificial mediums needed for routine use are not numerous. The 

 following kinds are useful. 



DEXTROSE AGAR 

 This preparation is intended for routine use in the isolation of fungi. 

 The only difference between this formula and that of Weidman's Pennsyl- 

 vania medium is the substitution of Difco peptone for Fairchild's peptone 

 and technical dextrose for the crude American variety, both changes being 

 without discernible sacrifice of any advantage. 





The pll is usually 5.8 to 6.2, although it is not necessary to be particular 

 about this. 



