THE PREPARATION OF CULTURE MEDIA 29 



then dilute 1 c.c. to 100 c.c. with sterile liquid, and 

 inoculate 10 tubes each with 1 c.c., each tube will con- 

 tain about 100 microbes ; inoculate 10 tubes each with 

 5 c.c., each tube will contain about 50 microbes ; in- 

 oculate 10 tubes each with *1 c.c., each tube will contain 

 about 10 microbes. Then dilute 1 c.c. to 1,000 c.c. with 

 sterile liquid, and inoculate 10 tubes each with 1 c.c., 

 each tube will contain about 10 microbes ; inoculate 10 

 tubes each with *5 c.c., each tube will contain about 5 

 microbes ; inoculate 10 tubes each with -1 c.c., each tube 

 will contain about 1 microbe ; inoculate 10 tubes each 

 with -05 c.c., each tube will contain about -5 microbes. 



Of the last ten tubes, then, about five only would 

 develop growths, and these would, in all probability, be 

 derived from a single microbe each, and thus be pure 

 cultures. 



Now although, in comparison with the gelatine-plate 

 method described below, this dilution process appears 

 tedious and troublesome, yet for the isolation of some 

 micro-organisms it is of the utmost importance, notably 

 in the case of those which, like the bacteria of nitrifi- 

 cation, refuse to grow on the ordinary solid culture 

 media. Later on will be found an account of Miquel's 

 application of this dilution process to water-examination. 



FIG. 5. H>-MATIMETEB (after Jorgensen). 



o, Glass slide on which the perforated glass square, b, is cemented so as to form an extremely 

 shallow circular cell, the depth of which is accurately determined once and for all. On 

 the glass bottom of this cell some very small squares of known dimensions are etched. 

 A small drop of the liquid in which the number of yeast-cells is to be determined is 

 placed in the cell, and the cover-glass, c, placed on the top so as to be in contact with 

 the liquid in the cell. The volume of liquid resting on each of the little squares can thus 

 be easily calculated, and by counting the yeast-cells visible with the microscope in each 

 square, the number in the .particular volume of liquid is determined. 



Hansen also successfully employed this dilution 

 method in his first preparation of pure cultures of yeast 



