GROWTH FACTORS 25 



discovery the interest of other workers was directed toward de- 

 termining- whether Wildiers' results could be confirmed, toward 

 learning whether other fungi have similar requirements, and 

 toward making attempts to discover the nature and properties 

 of bios. 



As the result of various researches it gradually became apparent 

 that bios is a complex, containing several growth factors. These 

 are now known to include biotin (vitamin H), thiamin (vitamin 

 Bi), pyridoxine (vitamin B ), /-inositol, /^-alanine, pantothenic 

 acid, and possibly sterol. 



The specific function of each of the bios components is not yet 

 satisfactorily known, although the complex has been subjected to 

 considerable study. From the attempts to learn their functions, 

 however, it may be concluded that they regulate respiration, re- 

 production, and rate of growth and that some act as coenzymes 

 and are essential in chemical syntheses effected by a particular 

 fungus. Not all species, however, seem to have identical require- 

 ments for growth factors. This observation has been interpreted 

 to indicate that the particular factor either is elaborated by the 

 fungus or else is not required at all. 



Copping (1929) found that certain wild yeasts, in a vitamin- 

 free synthetic medium, are able to elaborate their own growth 

 factors, whereas "domesticated" or "tamed" yeasts require that 

 the bios substances be supplied. 



Williams and Rohrman (1936) maintain that the minimum com- 

 plement of growth accessory factors required by yeast includes 

 aspartic acid, pantothenic acid, /-inositol, /3-alanine, and thiamin. 

 In their studies favorable growth responses with Trichophyton 

 inter digit ale occurred only upon the addition to the media of 

 pantothenic acid, riboflavin (vitamin B 2 ), thiamin, and /-inositol 

 [Mosher et al. (1936)]. 



Robbins and his associates (1942) found that Trichophyton 

 discoides, pathogenic to calves, suffers from complete deficiences 

 of thiamin, pyridoxine, and /-inositol. When from 1 to 10 m/x 

 moles of thiamin and pyridoxine and 0.1 to 0.5 mg of inositol were 

 supplied, maximum growth was secured. 



Hawker (1936) studied the influence of /-inositol isolated from 

 stale cultures of Botrytis cinerea and Gloeosporhnn fructigenum. 

 She also utilized baryta and an extractive of lentils to secure a pre- 

 cipitate containing /-inositol and a filtrate free from this factor. 



