8 PURE CULTURES OF 



method was materially improved by Koch. The latter at 

 first prepared his pure cultures in a somewhat imperfect 

 manner by means of streak cultures in nutrient gelatine 

 (1881). In 1883 this method was still generally employed 

 in his laboratory, and Hueppe also made use of it in his 

 investigations on the decomposition of milk by micro- 

 organisms (1884). In 1883 Koch published his improved 

 method of plate-culture, in accordance with which the pure 

 culture is prepared by introducing some of the micro- 

 organisms into fluid, germ-free, nutrient gelatine. After the 

 cells have been distributed in this mixture as equally as 

 possible by agitation, it is poured on to a horizontal glass 

 plate, also free from germs. This is finally covered over with 

 a moist bell-jar, and preserved in this manner at a suitable 

 temperature. It is assumed that each separate growth speck 

 which appears contains a pure culture. This is, however, by 

 no means always the case, for it is more difficult to separate 

 the cells from each other when they are in gelatine than 

 when they are in a liquid. In order to obtain an absolutely 

 pure culture with certainty, it is necessary, even when the 

 gelatine method is employed, to start from a single cell. 

 Hence I elaborated my new method by means of the moist 

 chamber (1883). 



A little of the nutrient gelatine containing the yeast cells 

 is placed on the under surface of the cover-glass of the moist 

 chamber (Fig. 2). Those cells are then accurately marked,* 

 the position of which is such that the colonies to which they 

 give rise can grow to their full size without coming into 

 contact with other colonies. For the subsequent inoculation 

 in a nutrient liquid medium, I only employed those colonies 

 which were proved, by direct microscopic examination to 

 have developed from single cells. 



The correctness of my results has been confirmed by 



* The object-marker of Klonne and Muller, of Berlin, may be recommended 

 for this purpose. 



