114 OUTLINES OF BACTERIOLOGY 



forms a red compound with nitrous acid, its presence in a nutrient 

 solution is easy to identify. This fact is made use of in the diagnosis 

 of those species that are known to produce indol. Fibrio cholerae, the 

 dreaded cholera organism, produces much indol, and it was in cultures 

 of this organism that the reaction was first observed. It is often in 

 consequence called the CJiolera-red reaction. Indol is also produced by 

 Bac. coli communis, a fact which is made use of, to distinguish this 

 organism, from Bac. typhosus, which it resembles in many respects. 

 Closely allied to indol, and smelling even worse, is Skatol. This 

 substance is formed towards the end of putrefaction, and together 

 with indol is responsible for the unpleasant smell of excrement. The 

 sulphur that is present in proteids appears in the end-products chiefly 

 as sulphuretted hydrogen or as methyl mercaptan. Other inorganic 

 end-products are marsh gas, free hydrogen, carbonic acid, free nitrogen 

 and ammonia, all of which are given off into the atmosphere in the 

 form of gases. Amongst the products of the decomposition of proteids, 

 mention must be made of the ptomaines that are produced from them. 

 These form a special class of organic substances, all containing nitrogen, 

 and having a high- molecular constitution as well as possessing a 

 number of physical properties in common, e.g. solubility in hot alcohol, 

 bitter taste, etc. A large number of these ptomaines have been found, 

 some of which are harmless and others very poisonous. Examples are 

 Neuridin (CjHj^^Nj), Trimethylamine (CjHgN) and Cadaverin (CjHj^Nj), 

 which are poisonous only in large quantities. On the other hand some 

 are extremely poisonous. 



Observations on Pure Cultures of Putrefactive Bacteria. By 

 observing the changes that take place in nutrient media, in which a 

 pure culture of one or other of the putrefactive bacteria is present, 

 it is possible to ascertain to some extent the changes produced by 

 the putrefactive bacteria in nature. This is indicated by the 

 following table : 



Organism Acting on Produces 



Proteus vulgaris Gluten and fibrin Phenol, Indol, Amines 



and Fatty acids. 

 ,, Casein Albumoses, Peptone and 



Amino-acids. 

 Streptococcus longus Fibrin Ty rosin, Leucin, Amines 



(anaerobic) and Fatty acids. 



Bacillus coli communis - Casein Albumoses. 



,, ,, Peptone Ammonia and Indol. 



„ „ Mixture of eggs and Skatol, Phenol, Aromatic 



flesh Oxy-acids, Leucin, etc. 



