VIABLE BACTERIA IN YOUNG CULTURES 407 



cally piano cemented coverslip for use with a ,!, inch objective, 

 was employed by Glynn, Powell, Rces and Cox, the organisms, 

 being examined in the stained condition under open illumination. 

 The indirect or viable count has, as a rule, been performed by 

 a modification of Koch's original plating method. The only 

 exceptions which need be noted are those of Naegeli and Schwen- 

 dener (1877) who took the amount of fermentation as their basis 

 for the computation of the number of growing organisms, and 

 Winterberg who accepted motihty as his criterion of liability. 

 The modifications of Koch's method have been concerned with 

 the medium used, the question of prehminary dilution, the 

 methods of dilution and the exact technique of counting the 

 plates. The majority of observers appear to have used agar, but 

 Buchner, Longard and Riedlin (1887), Hehewerth, Eijkman, 

 Zelikow, and Chick (1912), seem to have preferred gelatin, though 

 in some cases both media were employed. With regard to pre- 

 liminary dilution, the earUer workers generally preferred to plate 

 out the original emulsion, while of late the tendency has been 

 in the opposite direction, as in the case of Winterberg, Zelikow, 

 Mullcr (1895), Rahn (1906), Madsen and Nyman (1907), Lane 

 Claypon (1909), Penfold (1914), Coplans (1909), Chesney (1916), 

 and Noyes and Voigt (1916). The method of dilution has been 

 subject to considerable variation; on the whole volumetric 

 pipettes have been most popular, but Lane Claj^Don, Ficker 

 (1898), Chick, and Penfold used dropping pipettes, w^hile Hehe- 

 werth, and Graham Smith (1920) resorted to the use of a standard 

 platinum loop. Gotschlich and Weigang (1895) elaborated a 

 special technique in which dilution was performed by a combina- 

 tion of gravimetric and volumetric methods. The important 

 question of the counting of the plates has naturally depended 

 largely on whether or no a preliminary dilution of the emulsion 

 was made. Where the number of colonies was very great, micro- 

 scopic counting was adopted, usually with the aid of a Wolf- 

 hiigel's plate, as in the case of Buchner, Longard and Riedlin, 

 Where on the contrary, dilution was employed, the use of the 

 microscope was no longer necessary, and counting was perforaied 

 with the naked eye or with a magnif jdng glass — Kronig and Paul, 



