234 SUMxMARY OF CURRENT RESEARCHES RELATING TO 



Fermentation -^vill be apparent before the third day. Cultures thus 

 obtained can be poured on to the soil to be treated. 



Quantitative Estimation of Bacterial Mass by the Colorimetric 

 Method. *^ — J. Zelikow employs the colorimeter of Dubosc to estimate 

 the quantity of bacteria in a culture. The instrument (fig. 42) consists 

 of two beakers C to hold the stained solutions ; the niveaux are regulated 

 by the sinking of a polished glass prism T, the position of which is 



measured ; light is reflected from mirror M, 

 passed through the coloured solutions, and 

 then reflected by the prism P, so that each 

 beaker will correspond to one half of the 

 field of vision, and the absorption of stain in 

 the two columns of coloured solution may be 

 simultaneously compared. Two flasks of 

 bouillon are inoculated with culture ; after 

 24 hours the contents of one is passed 

 through a filter ; from the filtrate and also 

 from the unfiltered content of the other flask, 

 emulsions are made ; to definite volumes of 

 these, and also to the pure bouillon, definite 

 amounts of stain are added ; the whole is 

 heated at 70°-80° C. for an hour, and then 

 centrifuged ; the solutions are then drawn 

 off, and the amount of stain absorbed is 

 estimated by the colorimeter. The author 

 gives various precautions to be taken in 

 applying the method. 



Anaerobic Microbes of Water, f — H. 



Vincent advocates the following method for 

 enumerating and isolating the true anaerobic 

 microbes of water. The medium consists of 

 gelatin 50-75 gnu., glucose 5 grm., glycerin 

 5 grm., peptonised beef broth 500 c.cm., 

 the whole being neutralised, and at the time 

 of using a sufficient quantity of sulpho- 

 indigotate of soda is added. 

 Fig. 42. if tiie water is probably impure it is 



added to the medium in amounts of 0-05, 

 ■ 02, to • 01 c.cm. : if likely to be pure, in amounts of • 5, 1, or 2 c.cm., 

 the medium being previously boiled and brought to a temperature of 

 30°-35° C. The mixtures being made are then drawn up into 50 cm. 

 pipettes of diameter 3-4 mm. ; these when filled are sealed at both ends 

 and held in a stream of cold water to fix the gelatin. 



The strict anaerobes forming diffusely contoured, flocculent, granular 

 colonies, and secreting more gas, are readily distinguished from the 

 facultative anaerobes that form compact limited opaque colonies. 



* Centralbl. Bakt., Ite Abt. Orig., xlii. (1906) p. 476 (1 fig.), 

 t Ann. Inst. Pasteur, xxi. (1907) p. 62. 



