110 OUTLINES or BACTEBIOLOGY 



We may divide the bacteria that decompose proteids into two classes. 

 To the first belong those that decompose the naturally occurring pro- 

 teids into albumoses ^ and peptones,^ whilst in the second are included 

 those that attack these albumoses and peptones, decomposing them 

 into amino-acids. The amino-acids are then further decomposed by 

 various kinds of bacteria. 



The first class includes all the anaerobic bacteria that are saprophytic 

 (except Diplococcus magnus aerobius), Proteus vulgaris, Bac. fluorescens 

 liquefaciens, and Micrococcus pyogenes, whilst examples of the second 

 class are Bac. coli communis and Bac. prodigiosus. 



The amount and nature of the sugar content of a decomposing mass 

 are the chief factors which determine the course of decomposition. 

 The reason for this lies in the fact that bacteria change the sugars 

 into various acids, which very materially affect the growth of the 

 various competing bacteria. For whilst some are prevented from 

 developing or are even destroyed by the presence of a certain quantity 

 of acid, others are more resistant and are not hindered in their growth 

 by the presence of the same amount of the same acid. The more 

 resistant organisms obviously benefit by the weakness of the others. 



Whilst some of the saprophytic bacteria decompose only the proteids, 

 others attack only the sugars, and a third group attacks both the 

 proteids and the sugars. 



As explained, a mass of putrefying matter may be regarded as 

 an arena on which a number of bacteria are constantly struggling 

 to obtain the food contained in the matter. But the conditions 

 which make for success are constantly changing, because new 

 substances are continuously being produced by the activities of the 

 successful bacteria, which are generally unfavourable to their welfare. 

 Hence they disappear or become very much reduced in number, and 

 a new set of bacteria become masters of the situation, only to be in 

 their turn replaced by other competitors as further changes take 

 place. All the changes that take place in the organic matter are 

 in one direction, they consist, namely, in a breaking down of the 

 complex proteids and other materials into simpler substances, and 

 stop either when substances are at last produced which are unsuit- 

 able for bacteria to feed on, or when the percentage of acids formed 

 from the sugars is great enough to make bacterial life impossible. 



' Albumoses and peptones are derived from albumins. They possess the same 

 chemical structure and can be classed as albumins. They differ, however, from 

 the substances from which they are formed in being more soluble, and in possessing 

 different physical properties. 



