788 BACTERIA : THEIR WORK 



In addition to the compounds mentioned above as inter- 

 mediate between proteins and the simple gaseous end- 

 products of putrefaction, a great many other intermediate ones 

 are met with, namely, butyric and lactic acids, various organic 

 bases, as well as phenol, skatol, and indol, the two latter 

 being the compounds to which the characteristic odour of 

 faeces is due. 



Certain basic nitrogenous bodies resembling the vegetable 

 alkaloids, and known as ptomaines, are commonly produced 

 in the decomposition of meat, fish, and other albuminous sub- 

 stances by bacteria. A number of the ptomaines which have 

 been isolated are innocuous; others are, however, intensely 

 poisonous, and are the cause of the fatal effects following the 

 consumption of ' high ' game, imperfectly sterilised tiimed meats, 

 stale fish, decomposing cheese, meat pies, sausages, and other 

 putrefying foods. 



The amount and kind of the compounds produced in the 

 process of putrefaction depends upon the nature of the bacteria 

 causing it, and especially upon the free or restricted access of 

 oxygen to the substance undergoing change. Under anaerobic 

 conditions the foul-smelling compounds accumulate, whereas 

 when abundance of oxygen is present, and aerobic bacteria 

 allowed full play, a rapid oxidation of the sulphuretted hydrogen, 

 ammonia, and other offensive bodies takes place as soon as they 

 are formed, so that a foetid odour is scarcely noticeable under 

 these circumstances ; this inodorpus process of decomposition is 

 generally spoken of as decay. 



The commonest species of putrefactive bacteria are Proteus 

 vulgaris, P. mirabilis, and P. Zenkeri of Hauser, all of which, 

 with others, were formerly known under the collective name 

 Bac terium termo : they are all very minute organisms, possessing 

 extraordinary motile powers. 



Another putrefactive species present in the alimentary canal 

 of almost all the higher animals is Bacteri um colt commune. 



