68 BACTERIOLOGY. 



Most species of bacteria produce acids in the presence 

 of sugar, which explains the fact that neutral or slightly 

 alkaline cultures become acid at first from the small 

 amount of sugar contained in the meat used for making 

 the media. When the sugar is used up the reaction 

 often becomes alkaline, as the production of alkalies 

 continues after the acid formation has ceased. The 

 substances producing the alkalinity in cultures are 

 chiefly ammonia, amine, and the ammonium bases. 



The conversion of urea into carbonate of ammonia 

 affords special evidence of the production of alkaline 

 substances by bacteria: 



CO(NH 2 ) 2 -f 2H 2 CO 3 (NH 4 ) 2 



Urea. 2 Water. Ammonium carbonate. 



Leube has isolated several organisms from putrefy- 

 ing urine which separate ammonia from urea. The 

 power of decomposing urea, however, is not wide-spread 

 among bacteria. Out of twenty-seven organisms studied 

 by Wariugton, only two were found to decompose urea. 

 Of sixty species investigated by Lehmaun, three only 

 developed the odor of ammonia from sterilized human 

 urine. 



Ptomains Toxins. But beside ammonium carbonate, 

 a large number of basic crystalline substances have been 

 recognized, especially by Brieger, as products of bacterial 

 growth. These are now commonly known as ptoma'im, 

 or putrefactive alkaloids (from XTM/UX, putrefaction). 



Nencki, and then later Brieger, Vaughan and others, 

 succeeded in preparing organic bases of a definite chem- 

 ical composition out of decomposing fluids meat, fish, 

 old cheese, and milk undergoing bacterial decomposition 

 as well as from pure bacterial cultures. Some of these 

 were found to exert a poisonous effect, and for a long time 



