METABOLISM AND BIOCHEMICAL PROPERTIES 821 



of Br. abortus often have a rather greater resistance to thionin than abortus strains 

 from other sources. The Danish suis strains are more susceptible to all dyes than 

 the American suis strains, though their differential susceptibility is the same ; for 

 this reason they must be tested on plates containing only half the dye concentrations 

 just given. If reliance is placed exclusively on this method of differentiation, 

 confusion will not infrequently result between strains of different types. If on the 

 other hand, it is used, as we believe it should be used, in conjimction with other 

 methods, it will be found of considerable value. No other method, it may be noted, 

 is so useful in distinguishing between bovine and porcine strains. The method 

 has been subjected to some criticism (Saitta 1929, Meyer and Eddie 1930, Marshall 

 and Jared 1930, Cerruti 1932, Maggiora-Vergano 1932), but most workers have 

 reported on it very favourably (Kristensen and Holm 1929, Kristensen 1931, Taylor, 

 Lisbonne and Roman 1932, Grumbach and Grillichess 1932, Meyer and Zobell 1932, 

 Wilson 1933, Olin and Lindstrom 1934, Pagnini 1934, di Mino 1935). 



Resistance. — The members of this group exhibit the usual susceptibility of 

 vegetative bacteria to heat and disinfectants. In aqueous suspensions of moderate 

 density they are destroyed by heating for about 10 minutes at 60° C, and by 

 exposure for about 15 minutes to 1-0 per cent, phenol. In milk they are readily 

 destroyed by holder pasteurization. In agar cultures kept sealed at 0° C. they 

 generally live for at least 1 month, and often for considerably longer. Considerable 

 attention has been paid to their resistance under natural conditions, and much 

 information on this subject will be found in the Report of the Mediterranean Fever 

 Commission (1905-07). So many factors determine the exact outcome of any given 

 observation under natural conditions that it is dangerous to draw general conclusions 

 from the data so collected. In favourable circumstances, however, Br. melitensis 

 may remain alive for 6 days in urine, 6 weeks in dust, and 10 weeks in water or soil. 

 Br. abortus may survive for 7 months in infected uterine exudate kept at about 

 freezing-point (Bang 1897). In raw milk at room temperature it seems to die out 

 fairly rapidly with the production of acid. Acid production also seems to be the 

 cause of its rapid death in butter and cheese ; the organisms can rarely be found 

 in these articles for more than a few days (Smith 1934, Pullinger 1935). It may 

 live for a month in ice-cream (Thompson 1933). Br. suis may live on sacking for 

 4 weeks and in sterile faeces for 100 days in the dark (Cameron 1932, 1933). 



Metabolism and Biochemical Properties. — The effect of temperature and H-ion 

 conditions on growth has already been considered. All the members require the 

 presence of oxygen ; most strains of Br. abortus require in addition a partial 

 pressure of COj considerably higher than that found in atmospheric air. Under 

 ordinary aerobic conditions of incubation broth cultures become markedly alkaline, 

 owing to the production of ammonia. Litmus milk is turned weakly alkaline. 

 Occasional hsemolytic strains of Br. melitensis have been described (Forni 1927), 

 but usually neither the melitensis, abortus, nor suis strains have any lytic action 

 on blood. The effect of bile-salt on growth has not been studied fully ; on Mac- 

 Conkey's medium strains of Br. abortus, Br. melitensis, and Br. suis generally give 

 rise to small non-lactose-fermenting colonies after 3 or 4 days. 



In ordinary sugar media no fermentation is observable. Unlike most pathogenic 

 organisms, the members of this group are unable to produce obvious acid even from 

 glucose. However, quantitative observations have shown that some melitensis 

 and American sicis strains, if grown in 1 per cent, glucose peptone water, may utilize 

 5-20 per cent, of the glucose within a week, while abortus strains are unable to use 



