2 MICRO-ORGANISMS AND FERMENTATION. 



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 self-evident requirements of such in- 

 vestigations were put in practice, namely, that the first thing 

 to be ascertained, before drawing definite conclusions, must be 

 the point from which to start. 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 

 1.000 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 containing 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 modem 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 be observed only with difficulty or not at all. An 

 objection to these methods, urged with unquestionable 

 correctness, is that the violent treatment often alters the 

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

 On the other hand, it must be alleged that certain pathogenic 



