70 



ACTIVITIES OF BACTERIA. 



of the small amount of sugar in the bouillon (originating 

 in the meat). When the sugar is exhausted, then alkali 

 production advances more strongly (Th. Smith). 



The bodies causing the alkaline reaction, so far as known, 

 are ammonia (at times it may be smelt), amine, and am- 

 monium bases. To determine the amount of alkali formed, 

 one titrates single tubes which contain 10 c.c. of peptone 

 bouillon, both uninoculated and one to fourteen days after 

 inoculation, with decinormal acid, using phenolphthalein 

 as indicator. The difference upon titration gives the in- 

 crease of alkali. 



The following may be useful as an example of the pro- 

 duction of alkali by bacteria which, in the presence of 

 sugar, form acids energetically (for 100 c.c. amounting to 

 5 c. c. to 7 c. c. normal acid). One hundred c. c. of a nutrient 

 medium was employed, which contained a trace of meat- 

 sugar, and was originally exactly neutral with phenol- 

 phthalein. 



Inoculated with Bac- 

 terium coli. 



After Five 

 Days. 



0.1 normal 

 alkali. 



After Ten 

 Days. 



0.1 normal 

 alkali. 



After Fifteen 

 Days. 



0.25 normal 

 acid. 



A special instance of the production of an alkali by bac- 

 teria occurs in the transformation of urea into ammonium 

 carbonate, CO(NH 2 ) 2 + 2H0 2 =C0 3 (NH 4 ) 2 . 



In 1896 we stated that of sixty varieties tested, only the 

 Bact. vulgare, Bact. prodigiosum, and Bact. kiliense were 

 found able to decompose urea. Brodmeier (C. B. xvm, p. 

 380) has investigated the urea-splitting property quantita- 

 tively with the Bact. vulgare, and my pupil, Dr. Mann, 

 has recently done the same with the Micrococcus pyogenes 

 a aureus and y albus, with two forms of the colon bacillus, 

 and several sarcinse. One hundred c.c. of filtered urine, 

 sterilized at 85°, after being ten days in the incubator 

 contained abundant NH 3 . Mann could not demonstrate 

 any action by the same culture of the Bact. prodigiosum, 

 which we had previously found to cause energetic fermen- 

 tation of urea. Thus, this property also is variable, and 



