2 MICRO-ORGANISMS AND FERMENTATION. 



work was carried out without any proper precautions, as the 

 following example will show : 



Beer yeast was sown on a moist slice of bread ; the culture 

 was carefully covered with a glass shade, and all manner of 

 precautions were observed in order to protect the growth from 

 external contamination. After some days a growth of mould 

 appeared, as is always the case with moist bread ; and the 

 conclusion was therefore drawn that the beer yeast was the 

 origin of the mould, 'and that, consequently, yeast and mould 

 fungi were different phases of development of one and the 

 same species. 



A number of years elapsed before what are now universally 

 acknowledged to be the obvious requirements of such investiga- 

 tions were put in practice, namely, that the first thing to be 

 ascertained is the point from which to start before any con- 

 clusions can be drawn. This requirement was gradually defined 

 with greater precision, and at last, as we shall see later, a point 

 was reached which satisfies this demand in a higher degree 

 than has hitherto been the case in the allied branches of 

 science. 



A microscope capable of magnifying to the extent of 1000 

 diameters is, as a rule, necessary for the investigation of micro- 

 organisms. For the yeast and mould fungi the only preparation 

 generally required consists in placing a drop of the liquid con- 

 taining the organisms on an object-glass, and spreading it out 

 in a thin layer by means of a cover-glass. When cultivated 

 on solid substances, a very small portion of the growth is first 

 mixed with a drop of water. At any rate, the preliminary 

 examination of bacteria must always be performed in this 

 manner. 



In modern bacteriological research, and especially in the 

 case of pathogenic forms, a number of different methods of 

 drying and staining are employed, partly in order to facilitate 

 observation, and partly with a view to bring out characteristics 

 which would otherwise only be observed with difficulty or not 

 at all. An objection to these methods, urged with unquestion- 

 able correctness, is that the violent treatment often alters the 

 proportions of length, thickness, etc., of the bacteria. On the 

 other hand, it may be alleged that certain pathogenic forms 



