PRESERVATION OF CULTURES 59 



a superficial resemblance to it, or if no detailed examination of successive 

 transfers is made by a worker really familiar with the specific characters of 

 the stock strain. The physiological or biochemical investigator, obtaining 

 such a culture assumed as correctly named, will be seriously misled in the 

 interpretation of his experimental results. No culture should be used for 

 such an investigation without being fully identified at the outset and having 

 its proper appearance and reactions sufficiently studied to insure the relia- 

 bility of the results during the progress of the work. In other words, before 

 undertaking to do biochemical or physiological work, sound scholarship 

 calls for adequate precautions in the study and identification of the original 

 material supplemented by such mastery of its morphology and variability 

 as will insure its maintenance in proper condition. 



Mold Disease of A . niger 



A mold disease of Aspergillus niger is common in cultural study. The 

 colonies of the Aspergillus are overrun with an olive-green Penicillium 

 belonging in the Biverticillium group close to Penicillium rugulosum Thom. 

 This mold invades the mycelial felt, winds its hyphae within and about the 

 conidiophores, and fruits in a radiating series of short-stalked penicilli 

 surrounding the heads and upper halves of the conidiophores. This is 

 beautifully illustrated in figure 15, made by Edward Yuill and sent to us by 

 his brother John L. Yuill of Yorkshire, England. The black fruiting surface 

 may be completely covered with the olive-green conidial masses of the 

 Penicillium. If A. niger is grown in trays for acid formation, spots infected 

 in this way may be killed and disintegrated, thus interfering with fermenta- 

 tion, while the infected areas may be seen to drop out when the blanket or 

 felt of A. niger is lifted from the surface of the liquid. Other species when 

 inoculated have been irregularly affected, some strains of the same species 

 were attacked, whereas others were apparently immune. 



Bacteria 



Freedom from bacteria is essential to uniformity in the appearance and 

 in the reactions of molds. Colonies infected with bacteria may be un- 

 changed in character, but usually show marked physiological differences 

 when compared with colonies free from contamination. Associative action 

 may have important effects upon both organisms. Sartory (1920) dis- 

 cussed without identifying a species producing ascospores, but only when 

 accompanied by a particular bacterial associate. Nevertheless, a symbiotic 

 colony must not be allowed to masquerade as a pure culture representative 

 of a species. The next contaminated colony of the same species of mold 

 but with different bacteria may present a very different picture. These 

 conditions have been met often enough to make the emphasis upon freedom 

 from bacteria essential in study of this group. 



