BY H. GUEIG SMITH. 



73 



media, the differences in the acid-content of the cultures were 

 very small. Since acid in the culture would dissolve a certain 

 amount of calcium phosphate, the culture that contained most 

 acid would require the addition of most calcium chloride to 

 produce a certain effect. The relative acidities of the cultures, 

 however, were not sufficiently distinctive to account for the 

 difference in the amounts of calcium chloride necessary for com- 

 plete precipitation. The nature of the acid radicles in the 

 culture will probably explain the chief reason of the differing 

 susceptibility. That the bodies of the bacteria have only a small 

 function in the phenomenon is to be seen from the behaviour of 

 filtered cultures. Three cultures grown in ordinary neutralised 

 bouillon were filtered through porcelain filters and 2 c.c. portions 

 were treated with calcium chloride ( T ^ gram-molecule per litre) 

 clear supernatant fluids were obtained in one hour with the 

 following amounts of solution in c.c. : — 



Bad. typhi ... ... ... ... 04 



,, prodigiosum .. ... ... 0"8 



,, culi commune ... ... ... TO 



The differences are sufficient to indicate that it is to the pro- 

 duct of the bacteria that the phenomenon is due. I am of the 

 opinion that the cause may be traced to Bad. typhi withdrawing 

 less phosphoric acid from the medium than the other two 

 organisms which take up more and replace what they have taken 

 with other acids. These acid products of metabolism form with 

 calcium, insoluble salts which have less tendency to coagulate 

 into floccules than tricalcium phosphate. 



The differing susceptibility of Bad. typhi and Bad. coli com- 

 mune to calcium salts can be utilised to distinguish between them. 

 The method consists in pipetting two c.c. of a two or three days' 

 bouillon culture into a narrow test tube and adding one c.c. of 

 calcium chloride solution containing one gram crystallised calcium 

 chloride per 100 c.c The mixture is shaken and allowed to 

 stand for an hour. At the end of this time Bad. typhi shows a 

 well-defined precipitate, and in an almost clear supernatant fluid 

 several large floccules adhering to the walls of the tube. Bad. 



