224 TIIK IMIKNOMKNA OF IM'TRKFACTION 



five access. Titular distinctions have been employed to express these differ- 

 ences, 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 

 organisms. Of course both these processes may go on simultaneously in the 

 same substance, the outer surface, exposed to the air, decaying, whilst the 

 interior putrefies. This fact alone sufficiently proves how little value attaches 

 to researches wherein pure cultures are not employed. M. vox 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 attributable to several 



/O.HL 



compounds of the aromatic series. One of these is Indole, C 6 H / /CH, which 



\NH' 



combines as an imide with 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 cholera 3 asiatic<c 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 ^. BRIEGER (II.) in human 

 faeces, is almost invariably produced during the putrefaction of albumen; its 

 smell is even more repulsive than that of indole. A closely allied derivative of 

 skatole, viz., /3-methyl indole acetic acid, was discovered by M. v<>\ N i:\n\i 

 (IV.) among the putrefaction prod nets occasioned by JJacillus liqicefaciens magnus 

 in the absence of air. Phenol was first recognised as a product of album*-!! 

 putrefaction by E. BAUMANN (I.) in 1877, and orthocresol and paracresol by 

 E. BAUMANN and L. BRIEGER (I.) in 1879. The capacity of a large number of 

 (mostly pathogenic) species of bacteria for producing the above-named substances 

 was investigated by A. LEWANDOWSKI (I.). 



M. von Nencki and his pupils made a series of investigations on the products 

 of albuminoid putrefaction. Of their discoveries we will now briefly mention 

 those referring to leucine and tyrosine. These amido substances are secreted 

 by the pancreatic glands, and are almost always present in fresh freces. They 

 are also produced, under certain conditions, in the putrefaction of various albu- 

 minoids. Now, according to NEXCKI'S (V.) researches, leucine is further 

 decomposed by the activity of bacteria, the chief product being valeric acid, 

 along with carbon dioxide, hydrogen, and ammonia. The reaction is approxi- 

 mately expn ! by the equation 



('II., CH 2 ( -CH.NHo cooil | 2l!,.O = 



I.CIICJIIC. 



(CFL), = < II ' M.-COOH + CO, -f 2H, -f Nil . 



The decomposition "f ivio-inr nuy be cir.vtnl in two <liirTcnt ways: in 

 presence of air as was shown l.y K. I \.\ \ M \ \\ ( 1 1 .) the Nil, group is separated, 



