DEGRADATION OF THE ALBUMINOIDS. 291 



Physiology is not necessarily injured by the remark that, owing 

 to the employment of indefinite bacterial mixtures, these endea- 

 vours are not always free from objection from a bacteriological 

 point of view. 



In future researches into albuminoid decomposition or putre- 

 faction, it should always be borne in mind that here also the 

 co-operation and succession of various organisms (i.e. symbiosis 

 and metabiosis) will have to be taken into calculation. Until 

 this is done, mycological text-books will have nothing better to 

 offer than a varied collection of isolated observations, such as are 

 given in the following chapters and paragraphs. 



It has long been observed that the natural decomposition of 

 albumin yields malodorous gases and vapours when proceeding in 

 the absence of air, but that, on the other hand, these attendant 

 phenomena are wanting when air is allowed free access. Titular 

 distinctions have been employed to express these differences, the 

 natural inodorous decomposition of albuminoids being termed 

 decay, whilst the name of putrefaction has, in a narrowed sense, 

 been applied to the other set of phenomena. Formerly regarded 

 from the chemical standpoint alone, the fundamental physiological 

 basis of this differentiation has now been explained by the aid of 

 mycological research as follows : Decay is the result of aerobic 

 microbial activity ; putrefaction, of the energy of anaerobic organ- 

 isms. Of course both these processes may go on simultaneously 

 in the same substance, the outer surface, exposed to the air, decay- 

 ing, whilst the interior putrefies. This fact alone sufficiently 

 proves how little value attaches to researches wherein pure cultures 

 are not employed. M. VON NENCKI (III.) sought to explain the 

 putrefactive decomposition of the albuminoids as a process of 

 hydration, and cited in support of this view the observation that 

 the products obtained are the same as those produced by the action 

 of fusing caustic potash. 



The bad smell characteristic of putrefaction is often attri- 

 butable to several compounds of the aromatic series. One of 



CH 

 these is Indole, C 6 H 4 <( /CH, which combines as an imide with 



NH 



nitrous acid to form the red nitroso-indole. This property is 

 utilised for the detection of indole in cultures. Since a great 

 many bacteria are capable of producing a small (though sufficient) 

 quantity of nitrites in ordinary nutrient media, this characteristic 

 red coloration can be developed (in presence of indole) by slightly 

 acidifying the culture with sulphuric acid. Of the pathogenic 

 bacteria, Koch's Vibrio cholerce asiaticce was the first examined 

 for this reaction. This accounts for the current use of the term 

 "cholera red reaction," employed for this reaction by medical 

 bacteriologists. /3-methyl indole or skatole, which was first 

 discovered in 1877 by L. BRIEGER (II.) in human faeces, is almost 



