494 BACTERIOLOGY. 



entire surface forming a transparent scarcely visible growth. The 

 non-motile colon bacilli ( Emmerich, Havelburg), will form a small white 

 colony on the surface without any diffusion. .The motile colon bacilli 

 will diffuse, sometimes as rapidly as the Eberth bacilli, but unlike these 

 the growth will be opaque and easily visible- 



Hiss' Tube Medium. 



This is similar in composition to the above and contains 

 in addition 1 per cent of glucose. 5 g. of Liebig's meat ex- 

 tract, 5 g. of NaCl and 5 g. of agar are added to 1000 c.c. of 

 water. The mixture is heated till the agar is dissolved. 

 The water lost by evaporation is then replaced and 8 per 

 cent, of gelatin is added. When this has dissolved the solu- 

 tion is titrated. It is left acid but the acidity is reduced by 

 addition of N NaOH, so that it corresponds to 15 c.c. of nor- 

 . mal acid per liter. The liquid is then cooled to 60 D and 

 cleared by adding the white of an egg, previously beaten in 

 about 25 c.c. of water. The liquid is finally boiled for a 

 few minutes and iO g. of glucose are added. It is then sedi- 

 mented at 50, filtered through absorbent cotton, and then 

 through paper if desired. The clear filtrate is finally filled 

 into tubes and sterilized. 



Stab cultures of the organisms to be tested, are made 

 in this medium. The colon bacilli and B. icteroides give 

 rise to gas bubbles, whereas the Eberth bacillus does not 

 produce gas. Gas formation will be observed most satis- 

 factorily in about 8 or 10 hours after the tubes have been 

 placed in the incubator. The Eberth and the motile colon 

 bacilli diffuse through the medium, whereas the growth of 

 the non-motile colon and Eberth bacilli will be confined to 

 the line of inoculation. 



The difference in the transparency of the diffused 

 growths of the Eberth and colon bacilli as observed on 

 Stoddart's medium is not seen in this tube medium. It is a 

 convenient method, however, of demonstrating whether an 



