240 A MANUAL OF THE ASPERGILLI 



In the same way, extensive development of these forms as points of 

 infection in the lungs may give rise to conditions diagnosed as pseudo- 

 tuberculosis which may persist for long periods without resulting either in 

 death or complete recovery of the patient. Spores of A. niger are air 

 borne and hence are commonly drawn into the respiratory tract. They are 

 occasionally reported as causative agents in allergic reactions. 



Single Strain Cultures 



The great importance of some of the black aspergilli as fermentative 

 agents makes punctilious preservation of the actual strain employed the 

 only means either of insuring a process against breakdown or of intro- 

 ducing it in a new locality. Even when such a culture is maintained with 

 the utmost care, natural variation sometimes occurs. Induced variation, 

 such as that described by Steinberg and Thom in a series of papers (1939-40) 

 presents a further hazard in processes where cultures are grown at extreme 

 H-ion concentrations, or in the presence of chemical or other substances 

 which may actually be toxic at the concentrations employed. In a process 

 in one laboratory a strain appeared that presented a colony aspect in which 

 only a few typical black heads developed in a background of dwarfed and 

 fractional conidial fruiting structures. In another case, a mutant appeared 

 which differed so radically from A. niger in its secondary sterigmata and 

 spore chains that the Yuills described it as a new genus and species, Clado- 

 sarum olivaceum (Trans. Brit. Myc. Soc. 22: 194-200, Pis. 11-13. 1938). 



The user of one of these Aspergilli, then, needs to know his organism in 

 cultural aspect, in microscopic details, and in essential reactions in standard- 

 ized and reproducible substrata. Furthermore, he must be able to main- 

 tain it free from contamination with other species, and likewise free from 

 such variation, either natural or induced, as will interfere with consistent 

 and controlled results. 



