70 THE FLOCCULATION OP BACTERIA, 



Several circumstances were noted in the lime-water experiments. 

 The bacterial culture when neutralised to phenolphthalein with 

 sodium hydrate, was still alkaline when an equal and correspond- 

 ing quantity of calcium hydrate had been added. Taking 10 c.c. 

 portions, neutrality was reached with 2-35 c.c. tenth-normal soda 

 and 6-0 c.c. tenth-normal lime. Sterile bouillon made neutral to 

 soda was found to be still alkaline to lime, and as the latter was 

 gradually added a flocculent precipitate continued to appear 

 until neutrality was reached. This curious behaviour of lime and 

 soda suggested the presence of phosphates of the alkalies, a sus- 

 picion that was confirmed by testing the precipitate, which proved 

 to be tricalcium phosphate. The alkaline phosphates are derived 

 from the meat which forms the basis of the culture media, and 

 these are not completely precipitated when the media are neutral- 

 ised with soda. 



It is evident that this raises the whole question of precipitation 

 by calcium salts, since it is probable that the coagulum obtained 

 in the experiments consisted of bacteria entangled in a matrix of 

 calcium phosphate. This is all the more , probable, since the 

 precipitates were certainly more voluminous than could have 

 been expected from a simple flocculation of bacteria. On the 

 other hand, however, microscopical examination showed the 

 bacteria to be aggregated into large clumps, which would not 

 have obtained had they been simply caught in a coagulum. 

 Again, the trapping of the bacteria in calcium phosphate does 

 not explain the different sensibility of Bad. typhi as compared 

 with Bad. coli commune. It is true that the cultures were 

 differently acid, but this was not found to be so very marked, 

 10 c.c. of Bad. typhi culture being neutralised with 0'75 c.c, and 

 the same volume of Bad. coli commune or Bad. prodigiosum 

 culture with 0-90 c.c. tenth-normal soda. The relative acidity 

 would probably have been more marked had traces of glucose 

 been allowed to be present. The meat extract had been permitted 

 to begin a spontaneous bacterial growth, and consequently the 

 traces of glucose, that are generally present, had been eliminated. 



