DAIRY BACTERIOLOGY 



PART I 

 GENERAL 



Chapter I 

 Microorganisms and Fermentations 



BY microorganisms or microbes, we understand all organisms 

 which are too small to be seen by the naked eye ; they remained 

 unknown until it had become possible to construct strong magni- 

 fying glasses or the combination of lenses which make up the 

 microscope. Bacteria were first observed by the Dutch optician 

 Leeuwenhoek in 1675, but no real knowledge of their nature was 

 gained until the latter third of the last century, when Pasteur 

 carried out his classical researches. Bacteriology is thus a 

 comparatively new science ; nevertheless it has already revolu- 

 tionised both medical science and the technology of the fermenta- 

 tion industries, among which may be included the dairying 

 industry. 



As far as the fermentation industries are concerned, only three 

 groups of microorganisms come into consideration, Bacteria, 

 Yeasts and Moulds. Bacteria and yeasts proper are unicellular, 

 while moulds are generally multicellular . Unicellular organisms 

 may be united in chains, but the individual cells of the chain show 

 no differentiation as regards structure or function, excepting such 

 modifications as may be due to differences in age or nutrition. 

 In the moulds, on the other hand, it is possible to distinguish 

 between two groups of cells ; first, the mycelium, which is con- 

 cerned with the nutrition of the organism, forming a tangled 

 network in the nutrient medium, and second, the fine thread-like 

 shoots which bear the reproductive organs and generally project 

 out of the medium so that the spores may be carried away by air 

 currents (see Fig. 8). 



