YEASTS AND MOULDS. 587 



Aspergillus niger (Eurotium aspergillus niger, De Bary). 

 Dark chocolate-brown tufts. Conidia round, black-brown, or grey- 

 brown when ripe. This mould can be cultivated readily on bread 

 moistened with vinegar, on slices of lemon, and on acid fruits and 

 liquids. It nourishes best of all, according to Raulin, in a liquid 

 of the following composition : 



Grammes. 



Water 1500' 



Sugar-candy ....... 70* 



Tartaric acid ....... 4* 



Nitrate of ammonia ...... 4' 



Phosphate -6 



Carbonate of potassium ..... '6 



,, magnesium ..... '4 



Sulphate of ammonia . . . . . '25 



,, ,, zinc ...... '07 



iron -07 



Silicate of potassium ..... '07 



It was also found that the fungus grew best when the liquid 

 was spread out in a layer 2 or 3 cm. in depth in a shallow dish ; 

 and a temperature of 35 C. proved to be the most favourable. 

 The abstraction of zinc from the, nutritive liquid reduced the weight 

 of a crop from 25 (the average) to 2 grammes, and the presence 

 of T^OOOOO P art of nitrate of silver, or ^-^ part of corrosive 

 sublimate, stopped the growth altogether. It is saprophytic in the 

 living body. 



METHOD OF EXAMINING ASPERGILLUS NIGER. 



Species of aspergillus stain intensely with carmine, f uchsine or methyl- 

 violet ; but to examine Aspergillus niger with a high power a little 

 special technique is employed, as follows : A drop of glycerine is placed 

 on a clean slide, and a drop of alcohol on a cover-glass. With a fine pair 

 of forceps a few of the fruit-hyphae with their black heads are immersed 

 in the alcohol. The cover-glass is then turned over on to the drop of 

 glycerine, and the slide held in the flame of a Bunsen burner till the 

 spores or conidia are dispersed. To make a permanent preparation 

 remove the cover-glass, and transfer the fruit-hyphae so treated to a 

 mixture of glycerine and water (1 to 5) ; a drop may be conveniently 

 placed ready on a slide provided with a ring of Canada balsam. The 

 specimen is then, permanently mounted by employing a circular cover- 

 glass, and surrounding it with a ring of cement in the usual way. 



