8 An Introduction to Medical Mycology 



Fungi, however, vary considerably according to the species. The normal 

 habitat of some of the lower fungi is in the depth of a body of water. 

 Others grow well on the surface of a liquid medium. Most pathogenic 

 species of fungi grow best on a semisolid or solid stratum. Fungi may 

 remain dormant for some time under natural or artificial conditions of 

 diving, being capable of revival with the addition of moisture. 



3. OXYGEN 



With the exception of Actinomyces bovis, the common pathogenic fungi 

 require oxygen for life and development. Lacking sufficient oxygen, repro- 

 ductive bodies are sparse; they may be stimulated to develop by an excess 

 amount of oxygen. 



4. LIGHT 



In some mycoses, such as tinea versicolor, the eruption is almost invari- 

 ably confined to a covered portion of the body. The fungicidal action of 

 certain light rays has been considered as a possible explanation. In our 

 experience the growth of fungi has been almost equal in absolute darkness, 

 subdued light and bright light. Certain ultraviolet rays have an inhibiting 

 but not lethal effect. In our hands roentgen rays and radium have had little 

 action as lethal agents, although some observers have reported inhibitory 

 action on certain fungi. 



5. NITROGEN REQUIREMENTS 



The manner in which the dermatophytes utilize the amino acids in 

 keratin has been the subject of considerable speculation and some careful 

 research. A characteristic of all keratin is its chemical stability. According 

 to Nickerson and Williams, no enzyme has yet been found that actually 

 hydrolyzes a keratin. They believe it is possible that the dermatophytes 

 act on keratin not through primary enzymatic digestion but secondarily by 

 enzymatic attack on a reduction product, as shown for the clothes moth. 

 In culture mediums, the usual source of nitrogen is a peptone. All peptones 

 are complex, containing inorganic compounds, variable amounts of amino 

 acids, protein split products and other substances with growth-producing 

 capacities. Mosher, Saunders, Kingery and Williams found that Tricho- 

 phyton gypseum would not grow on a medium containing only inorganic 

 nitrogen. Successful growth in a synthetic medium was possible only if 

 amino acids were added. These authors, as well as Robbins and Ma, deter- 

 mined that a suitable mixture of amino acids promoted growth better 

 than a single amino acid. The latter authors found that the fungus could 



