CHAPTER XXIX. 



BIOLOGICAL AND SANITARY MATTERS. 



The Decomposition of Milk Micro-organisms. The decom- 

 position of milk is due to the action of micro-organisms. The 

 description of their life-history, and the means of separating 

 and identifying them belong to the science of Bacteriology. 

 The following slight sketch will, however, be found of use to 

 the dairy chemist : 



Classification: Micro-organisms belong to the vegetable 

 kingdom, and are classed among the fungi ; they are divided 

 into 



Schizomycetes or fission fungi. 



Saccharomycetes or yeasts. 



Hyphomycetes or moulds. 



The Schizomycetes are again divided into families according to 

 their shape and mode of growth : 



Bacteria ; short rod-like forms forming no spores. 

 Bacilli ; rod-like forms forming spores. 

 Spirilla ; curved rod-like forms. 

 Micrococci ; round forms occurring singly. 

 Diplococci ; double. 



Staphylococci ; in bunches. 

 Streptococci ; growing in chains. 

 Sarcince ; ,, in groups. 



Leuconosioc ; thread-like forms. 

 Cladothrix ; branching forms. 



The distinction between these forms is by no means absolutely 

 defined ; thus many species forming spores with difficulty or 

 only under certain conditions, which were formerly classed as 

 Bacteria, are now called Bacilli. Some organisms grow as 

 micrococci, streptococci, spirilla, and leuconostoc. 



Action on Milk. 



For the purpose of the dairy chemist micro-organisms may 

 be classed according to their action on milk, as follows : 



Those acting on milk-sugar (a) producing lactic acid ; 

 (&) butyric acid 



(c) alcohol. 



444 



