132 OUTLINES OF BACTERIOLOGY 



That the rise of temperature in these processes is, partly at least, 

 due to microorganisms may be gathered from the fact that the rise does 

 not occur if the material be sterilised before being massed together. The 

 spontaneous heating of hay and of cotton-waste has been studied more 

 closely than most of the other processes of a similar nature. A rise of 

 temperature occurs in moist cotton-waste only if oxygen be present, so 

 that the development of heat, in the initial stages, has been ascribed to 

 aerobic organisms. The temperature rises to 67° C, and the cotton- 

 waste becomes converted into a humous mass from which vapours of 

 trimethylamine are given off. Very little is known of the specific 

 organisms which help to cause this development of heat. 



The spontaneous heating which occasionally takes place during 

 malting, as a result of bad management, is probably due to the 

 activity of a mould called Aspergillus fumigatus. The temperature 

 rises to 60° C. and higher, and there can be no doubt that the diastatic 

 power of the malt is in consequence seriously impaired. The most 

 successful of the researches on this subject has been in connection with 

 the spontaneous heating of moist hops. From the warm mass a 

 microbe has been isolated, and studied in pure cultures. This has 

 been named Bacillus lupuliperda. The individuals comprising this 

 species are 0-7 /^ in breadth and from 0'7 to 2 5 /«. in length: they 

 are motile under normal conditions. The microbe thrives well in 

 hop-extract, excreting large quantities of trimethylamine. In the 

 presence of sugar the cultivating medium is acidified owing to the 

 production of butyric acid. Bac. lupuliperda also liquefies gelatine. 

 Its normal habitat is the soil, from which it enters into the hop, and 

 if during storage the hops are massed together in a damp condition, 

 this microbe multiplies rapidly. The result is spontaneous heating, 

 which greatly deteriorates the value of the hops. Although this 

 microbe has not been isolated from hay, it is very probably an active 

 agent in the spontaneous heating of this substance, as, here also, 

 under the same circumstances, large quantities of trimethylamine are 

 produced. At the same time it must be mentioned that the 

 spontaneous heating of hops is not always, if ever, solely occasioned by 

 the activity of Bac. lupuliperda, as other organisms have been isolated 

 from decomposing hops. Thus a yeast allied to Saccharomyces Lud- 

 wigii has been isolated, as well as several moulds, e.g. Aspergillus 

 glaucus, Penicillium glaucum, Rhizopus nigricans, and Oidium humuli. 

 Aspergillus glaucus and Penicillium glaucum use up the organic acids 

 of the hops, as well as their sugar, so that they render the reaction of 

 the hops, which is acid in its normal condition, alkaline. 



