TEXT-BOOK OF BACTERIOLOGY. 363 



should be mentioned, which thrive at ordinary room-temperature; 

 also the niger, thriving at breeding heat. 



ASPERGILLUS PLAVESCENS. 

 The pathogenic Aspergillus flavescens grows almost exclusively 

 at high temperatures; it is distinguished by large, strong "fruit- 

 heads " and the greenish-yellow color of its cultures. It exhibits 

 on the plate (like all the aspergilli), even with slight magnifica- 

 tion, the fructifying organs densely covered with sterigmata and 

 their spores resembling little thorn-apples." 



ASPERGILLUS FUMIGATUS. 

 Aspergillus fumigatus has exceedingly delicate and neat " fruit 

 heads " and at breeding temperature forms a film, at first bluish- 

 green and afterward ashy-gray. This film never extends far from 

 the surface of the gelatin. Its germs are widely diffused and very 

 frequently found in our common bread. In the incubator, non-ster- 

 ilized bread-paste is almost regularly covered with a dense culture 

 of this mould in a very few days. 



MUCOR MUCEDO. 



The Mucor mucedo is the best known among the mucorinefe; it is, 

 next to the Penicillium glaucum, the most common mould. It only 

 grows at ordinary temperature, and, on the gelatin plate, quicklj' 

 forms dense, luxuriantly growing films, whose black poppy -seed- 

 sized " fruit-heads " can easily be perceived with the naked eye; when 

 magnified they appear as smooth, round structures. On bread- 

 paste there is developed a dense j'ellowish-brown growth of filaments 

 shooting upward like a miniature forest. 



The Mucor stolonifer has a still more striking growth and usually 

 develops mycelium growing to some distance from the surface of 

 the culture medium. 



The species Mucor corymbifer and M. rhizopodiformis, de- 

 scribed by Lichtheim, are pathogenic. Grown on bread in the incu- 

 bator, the former appears as a dense snow-white lawn or film, look- 

 ing like plucked cotton. M. rhizopodiformis grows lower and has 

 black fruit-heads; it is readily recognized by a peculiar ethereal 

 or aromatic odor in bread cultures, presumably caused by the fer- 

 mentation of this medium. 



OIDIUM LACTIS. 



The Oidium lactis belongs to the class of simple mycelial fungi 

 destitute of germinative organs. 



It is found in nearly all milk, especially when it begins to sour. 



