38 VARIATIONS IN THE LOWER FUNGI 



neously. Variations are much more likely to occur in old laboratory 

 strains than in recently isolated cultures. Although it is true that 

 instability is more likely to appear in a strain which has been fre- 

 quently transferred than in one which has been subcultured only at 

 long intervals, it is also true that, once instability occurs, the degree 

 of variation is increased if the culture is allowed to grow for a long 

 time in a single culture, as in giant colonies. Thus staling of the 

 medium and aging of the organism appear to be potent factors. 

 Variants have been described more frequently in parasitic species 

 than in saprophytic ones, but this may be due merely to the fact 

 that mycologists have been more interested in pathogenic species. 



Induced Variations. Little work has been done on the deliberate 

 production of variants in fungi by the action of external agents. 

 Barnes - reported the development of variants of Thamnidium ele- 

 gans, Botrytis cinerea, and Eurotium herbarium (resulting from the 

 application of heat to the spores). Dickson,^° working with species 

 of Chaetomium, and Nadson and Philippov -^ with Mucorales, ob- 

 tained variants from the action of x-rays. Haenicke " obtained 

 variants of Penicillium species by adding poisons to the medium. 

 Emmons and Hollaender " reported very precise experiments upon 

 the production of mutants of Trichophyton metagrophytes {T. gyp- 

 seum) by the action of ultraviolet light. They found that the 

 mutants observed were similar to those that occur spontaneously, 

 and stated that the ultraviolet light accelerates the rate of mutation. 

 They found that the percentage of mutants among the progeny of 

 the surviving conidia increased with the duration of exposure up to 

 a certain point (at which only about 8 per cent of the spores were 

 still alive) ; with longer exposures and lower survivals, the propor- 

 tion of mutants decreased. Negroni ^* produced rough type colonies 

 of Candida albicans by the use of immune serum, a procedure which 

 has been very fruitful in inducing the S ^ R transformation in bac- 

 teria. 



Variations in Infection. There is some evidence that variations 

 may occur in the tissues in fungus diseases. Thus Weidmann -^ re- 

 ported a case of trichophytosis of the feet. Cultures were taken over 

 a period of years. At first an organism downy in appearance, and 

 identified as Trichophyton inter digitate, was obtained regularly in 

 cultures. But after five years a fiat powdery type of colony, T. 

 mentagrophytes, appeared. I have been greatly impressed by ob- 

 servations which I have made on organisms isolated from two cases 

 of moniliasis. In one case, an adult, a chronic pulmonary infection 

 was followed by multiple abscesses through the body. From the 



