26 rri/ri'RK METHODS AND TECHNIQUE 



upon to determine the composition. These media are, however, 

 important in all culture work. The following solution has been in 

 such common use as to be generally designated a standard nutrient 

 solution : 



Ammonium nitrate i.o gram 



Dihydrogen potassium phosphate 5 gram 



Magnesium sulfate 25 gram 



Iron chloride ' trace 



Cane sugar 5.0 grams 



Water 100 cc. 



With some fungi the addition of a small quantity of sodium chloride 

 is advantageous. 



Among the many ofher culture fluids which have been used, 

 one of the most important available alike for fungi and bacteria, 

 although not ideally constituted, is Uschinsky's solution, made of : 



Ammonium lactate .... 6-7 grams 



Sodium asparaginate 3-4 grams 



Potassium hydrogen phosphate 2-2.5 grams 



Magnesium sulfate 0.3-0.4 grams 



Sodium chloride 5-7 grams 



Calcium chloride o. i gram 



Glycerin 30-40 grams 



Distilled water I ooo cc. 



Experience in culture work will promptly demonstrate that the 

 concentrations of the above solutions are to be regarded as impor- 

 tant because they establish standards. In special cases, however, 

 it may be desirable to increase considerably the amount of carbo- 

 hydrate, and this, in turn, may render desirable further changes. 



SOLID MEDIA 



Nutrient agar agar. Agar, or agar agar, is a substance some- 

 what of the nature of gelatin. It is, in fact, a kind of gelatin, or 

 glutinous substance, made from certain seaweeds, especially species 

 of Gelidium (Fig. 6) or Gloiopeltis, which grow abundantly on the 

 coasts of Japan and China. The commercial article is usually ob- 

 tained in the form of shred-like strips, or as a powder. Agar has 

 this advantage over gelatin, namely, that at a suitable strength it 

 will remain solid up to a temperature of at least 95 C. , and it 



