32 MEDICAL MYCOLOGY 



ties. The optimum humidity seems very closely related to oxygen supply and 

 respiration. Many of the lower fungi grow well, or even normally are found, 

 immersed in water. Many others will form a thick hyphal mat over the sur- 

 face of a liquid culture medium, although in this case much more oxygen is 

 required for normal development than in purely aquatic fungi and the repro- 

 ductive structures are usually produced in the aerial mycelium. Still other 

 groups will grow well and reproduce only on solid substrata, and a few grow 

 best in comparatively low humidities. Growth is usually much slower at low 

 humidities.* Some species have a narrow range while others will tolerate 

 a very wide range. 



Transpiration rates and humidity are often important in initiating repro- 

 duction. Very frequently reproductive structures are produced only when 

 vegetative growth is severely checked by the drying out of the media. This, 

 however, is usually associated with partial exhaustion of nutrients and the 

 accumulation of toxic products of metabolism (staling) so that it is often 

 difficult to evaluate the influence of the various factors. (Klebs 1896, Coons 

 1916.) 



Nutrition. — The most emphasis has been placed upon this factor and a 

 great body of literature on culture media and their effects has been produced. 

 The complexity of the vast majority in use does not lend itself to an analysis 

 of the separate factors involved. These may be considered under the head- 

 ings of inorganic salt requirements, carbon and nitrogen supply, and relations 

 to concentration of hydrogen ions, although these are closely interdependent 

 and also related to the physical factors of the environment. 



Inorganic Salts. — The requirement of these seems much the same as for 

 the higher plants, traces of potassium, magnesium, iron, and calcium being 

 necessary to secure good growth and reproduction. Calcium, however, is 

 much less important for fungi than for the flowering plants. Of the nonmetal- 

 lic elements, phosphorus, sulphur, carbon, and nitrogen are important. Other 

 elements are often present and may influence growth and reproduction, but 

 they are relatively unimportant in comparison with the above (e.g., McHargue 

 & Calfee 1931). Phosphorus is usually supplied as a phosphate, where it is 

 often useful in regulating the concentration of hydrogen ions in the solution. 

 In many media it is supplied as nucleoproteins, nucleic acid, and lecithin, and 

 seems equally available in these forms. 



Sulphur. — This element is usually supplied as a sulphate, but is also 

 utilized from sulphocyanates, thiosulphates and the sulphur-containing amino 

 acids and their compounds. The literature on this subject was well sum- 

 marized by Armstrong (1921) and will not be covered here. In various or- 

 ganic media probably a large portion of the necessary sulphur is available 

 from the proteins since practically all of them contain some cystine or cysteine. 

 Where large amounts of sulphur are available, particles of sulphur may be 



♦This fact may b© utilized in stock cultures by transferring to a 4-5% agar instead of 

 l%-3% commonly employed. Since growth is slow and, water loss is slower from the harder 

 agar, one safely can allow a much longer time to elapse between transfers. 



