34 MICRO-ORGANISMS AND FERMENTATION. 



was 100 colonies from 108 cells. This proves the plate 

 method to be faulty also in the case of yeast. 



Thus, the advantage of HANSEN'S method over KOCH'S 

 for the pure cultivation of yeast is, that it has a certain 

 starting-point. Even if the plate cultures are repeated 

 several times, one can never be certain whether the desired 

 result has been attained or not. With regard to the 

 bacteria, however, it is generally impossible to secure a 

 starting-point from one individual cell. In such cases 

 KOCH'S plate culture is still the best method we have. 



8. COUNTING THE YEAST-CELLS. 



In the yeast and spirit manufactures it is of impor- 

 tance to determine the multiplying capacity of the yeast- 

 cells during the growth of the yeast. This must naturally be 





FIG. 10. Hsematimeter : a, object-glass ; b, cemented cover-glass with circular opening ; 



c, cover-glass. 



effected by a direct counting of the number of cells which 

 occur in a determinate volume of the liquid at different 

 stages of the fermentation. Experiments having this object 

 in view have been undertaken especially by DELBRUECK, 

 DURST, HANSEN, HAYDUCK, and PEDERSEN, whilst FITZ has 

 applied the method of counting to bacteria. 



The counting is performed by means of an apparatus 

 constructed by HAYEM and NACHET (Fig. 10), which was first 

 employed for counting the corpuscles of blood (hence termed 

 Jicematimeter). The late Prof. PANUM, of Copenhagen, was 

 the first to employ this apparatus for counting micro- 

 organisms, in order to determine their multiplying capacity. 

 The hsematimeter consists, as shown in Fig. 10, of an object- 

 glass on which a cover-glass of known thickness (0*2 mm., 



