44 MICRO-ORGANISMS AND FERMENTATION. 



As early as 1821, Ehrenberg observed the germination of 

 the spores of certain fungi by careful observations of this kind. 

 The propagation of yeast cells was observed by Mitscherlich 

 (1843), Kiitzing (1851), and F. Schulze (1860), in the same 

 way. A small quantity of top yeast was diluted with beer- 

 wort until it contained only one or two yeast cells ; from a 

 drop of this an ordinary preparation was made, the cover- 

 glass was cemented on to the glass slide, to prevent the evapor- 

 ation of the drop, and the development of the cell was watched 

 under the microscope. Similar cultures were employed by 

 Tulasne (1861) and de Bary (1866), in their famous researches 

 on the germination of spores. A considerable improvement 

 in the method was made by Brefeld during his detailed re- 

 searches on mould, blight and mildew fungi, in which he 

 followed the development of the mycelium until it, in its turn, 

 again formed spores. The infection on the object glass was 

 protected by means of a small shield of paper fastened on to 

 the tube of the microscope, and this was afterwards converted 

 into a moist chamber (1881), after Brefeld had recognised the 

 danger of foreign germs penetrating into the cultures. He 

 diluted the material with water, brought a drop containing a 

 single germ on to the cover-glass, added some nutritive 

 liquid containing gelatine, and placed the cover-glass, with 

 the drop underneath, on to a glass ring (Bottcher's chamber), 

 which was fastened to the object glass. As the apparatus 

 and the nutritive liquid were sterilised, all the necessary 

 conditions were fulfilled for carrying out a culture experiment 

 without contamination. We may here see how improved 

 methods of cultivation have led to the preparation of an 

 absolutely pure culture. By the help of his cultures Brefeld 

 made the interesting observation (1883) in quite a number of 

 fungi e.g., the smut of wheat, the boil-blight of maize, 

 etc. that the conidia are able to propagate by direct budding, 

 like yeast, without throwing out new seed-carriers. 



A short survey follows of the different methods which 

 have been applied for preparing pure cultures on the large 

 scale. 



(a) Physiological Methods. At the earliest stage, attempts 

 were made to reach the goal by calculating the probabilities, 



