194 MICRO-ORGANISMS AND FERMENTATION. 



extends and throws out on all sides branched filaments, which 

 dislodge the inner layers of the envelope. These branches 

 finally take the form of an ascus (M and A], eight spores being 

 formed in each. After the breaking up of the asci the spores 

 lie loose in the interior of the perithecium, and are liberated 

 by the rupture of its fragile wall. The spores are bi-convex, 

 and carry a longitudinal furrow ; they possess an opaque 

 outer membrane and an inner one, which on germination 

 bursts the outer membrane, forming two valves (r). This 

 species thrives best at a temperature of about 25 C. The 

 enzymes that are associated with Aspergillus glaucus are, 

 amongst others, diastase, invertase, maltose, and a proteo- 

 lytic enzyme. 



Another well-defined form is A. flavus, with a yellowish- 

 green mycelium occurring frequently on bread, and also on 

 dry excrement. Its optimum temperature is at 37 C., and 

 it is believed to be pathogenic, its presence having been detected 

 in the human ear. Its conidia are usually smooth. 



A. fumigatus occurs on very different substrata, and is 

 also pathogenic both to man and beast. It forms a greyish 

 or greyish-green vegetation, and has an optimum temperature 

 at 40 C. It produces minute conidiophores with small 

 spherical conidia and brown perithecia. It contains the same 

 enzymes as those occurring in A. glaucus. It plays a part in 

 the spontaneous ignition of dry vegetation, and may, according 

 to Cohn, cause a rapid rise of temperature in green malt. 



A particularly interesting form of Aspergillus is A. (Sterig- 

 matocystis) niger, which produces branched sterigmata. It is 

 of very general occurrence, and forms blackish-brown patches 

 of conidiophores together with spherical, smooth or warty 

 conidia. It also produces yellowish sclerotia (without spores). 

 Its optimum is at 40 C. It grows well in an extract of oak 

 galls, and in a tannic acid solution. It is of technical im- 

 portance, as it is used in the preparation of gallic acid from 

 tannin. According to Fernbach and Pottevin, a special 

 enzyme secreted by the fungus is active in this process. It 

 is produced only on substances containing tannic acid, and 

 has its optimum at 67 C. Wehmer has shown, moreover, 

 that when grown on carbohydrates, such as grape sugar, A. 



