ESSENTIAL HON METALLIC ELEMENTS 111 



duces a volatile, toxic, organic arsenic compound, trimethylarsine, 

 (CH3)3As, which has an odor resembling garlic. In the past P. hrevicaule 

 has been recommended for the detection of arsenic compounds in forensic 

 medicine. This microbiological test for the presence of arsenic is said to 

 ))e many times as sensitive as the ]\Iarsh test. The early work on the 

 utilization of arsenic compounds by fungi is reviewed by La Far (1911) 

 and more critically by Challenger et al. (1933). P. hrevicaule also pro- 

 duces dimethyl selenide from selenium compounds (Challenger and 



North, 1934). 



SUMMARY 



The classification of essential elements as structural or functional may 

 be misleading in that an element usually plays many roles. This is 

 especially true of the essential nonmetallic elements. 



With the exception of carbon dioxide all the organic compounds used 

 by or contained in fungi contain hydrogen. One of the most important 

 hydrogen-containing compounds is water. This compound is associated 

 with proteins in the form of bound water, and it functions as a solvent in 

 which most if not all biochemical reactions take place. Water enters 

 into many reactions, particularly in the hydrolytic processes of ''diges- 

 tion." Apparently fungi do not utilize free hydrogen. 



None of the fungi appear to be obligate anaerobes. Many are faculta- 

 tive anaerobes, while some appear to be strict aerobes. Free oxygen is 

 used by the fungi in respiration, chiefly as an acceptor of hydrogen. The 

 facultative anaerobes have another mechanism of oxidation which does 

 not involve free oxygen. This is called anaerobic respiration, or fermen- 

 tation. The rate and amount of growth and sporulation and the meta- 

 bolic by-products of a given fungus are affected by the oxygen supply. 



The problem of specificity arises in connection with the form of sulfur 

 utilized. Most fungi utilize sulfate sulfur, but some require reduced sul- 

 fur. Other species are unable to synthesize specific sulfur-containing 

 amino acids, especially methionine. Sulfur enters into the composition 

 of enzymes and other proteins, peptides, and at least two vitamins. 



The fungi utilize phosphorus in the form of phosphate salts and esters. 

 Some specificity in the different sources of phosphate has been found 

 Phosphate esters enter into a wide variety of enzymatic reactions, and 

 many coenzymes are phosphate esters. 



It is thought that certain phosphate esters act to transfer chemical 

 energy to certain enzymatic reactions. Phosphorus enters into the com- 

 position of proteins, especially the nucleoproteins, which are found in the 

 nucleus or cytoplasm of every cell. Viruses and genes are thought to 

 consist largely of nucleoproteins. 



Fungi differ in ability to utilize different forms of nitrogen. A few 

 utilize atmospheric nitrogen; many utilize nitrate nitrogen; and a still 



