74 THE FLOCCULATION OF BACTERIA. 



coli commune, on the other hand, has an ill-defined precipitate 

 and a very turbid supernatant liquid. 



From these numerous experiments I have shown : — 



1. That bacteria are not flocculated by salts of potassium, 



sodium or ammonium like particles of suspended inorganic 

 mattei*, and consequently that a pure flocculation or 

 coagulation cannot be employed as a means of separating 

 bacteria from cultures or of causing ultra-microscopical 

 bacteria to cohere into visible cell-aggregates. 



2. That salts of lime form a precipitate of calcium phosphate 



with the phosphoric acid of the medium. 



3. That, since all ordinary media contain phosphates, and the 



organisms grown therein always retain traces of phosphoric 

 acid, any substance capable of forming an insoluble phos- 

 phate will, when added to bacterial suspensions, r:ause a 

 precipitate to form, and this, by entrapping the bacteria, 

 will produce an apparent flocculation of the organisms. 

 Microscopical examination may not indicate the presence 

 of a precipitate because some insoluble phosphates, as for 

 instance tricalcium phosphate, appear like large bacterial 

 clumps. 



i. That bacteria when grown in ordinary media exhibit 

 different powers of precipitation with calcium salts, 

 Bad. typhi requiring only one-fifth the amount required by 

 Bad. coli commune. 



5. That calcium chloride can be employed as a means of dis- 

 tinguishing between these two organisms. 



