BY R. GREIG SMITH. 69 



The action of sodium salts. — I have previously found common 

 salt to have rather a weak action, but as it occurs in most media, 

 and is frequently quoted as a flocculating- agent, it was used upon 

 these experimental bacteria. There was no flocculation, however, 

 with small quantities. Larger quantities gave a similar result 

 even when the salt was added in proportions varying from 550 

 to 7,700 milligrams of sodium per 100 c.c. and the tests were 

 allowed to stand for 24 hours. Since this is equal to nearly 20 

 per cent, of common salt, it is evident that sodium salts do not 

 flocculate bacteria. 



The action of potassium and ammonium salts. — Although the 

 action of these is much superior to sodium salts, no flocculation 

 was obtained, and in the case of potassium chloride even when 

 24 per cent, was present. It can, therefore, be said that these 

 salts do not flocculate bacteria. 



The action of peptone. — This is not recognised as a flocculating 

 agent, but since bouillon cultures contain 1 per cent, and bacteria 

 are generally found more or less precipitated in bouillon cultures, 

 a trial with it seemed advisable. As no coagulation appeared 

 even when the culture contained 10 per cent., its use as a floccu- 

 lating agent may be discounted. 



The effect of temperature. — It is a well-known fact that heating 

 causes the rapid precipitation of many chemical precipitates. 

 Extreme temperatures cannot be employed in working with 

 living bacteria, and the range between room temperature and 

 blood heat was found to be too narrow to show any difference in 

 the precipitation of the cultures with calcium chloride. 



The action of lime water. — Whilst the hydrates of potassium 

 and sodium prevent the flocculation of inorganic particles, hydrate 

 of calcium greatly assists flocculation. This fact was remembered 

 when calcium chloride was chosen in these experiments. When 

 a solution of calcium hydrate, containing 2 milligrams of calcium 

 per c.c, was gradually added to a culture of Bad. prodiyiosum, a 

 precipitation occurred. This was complete in half-an-hour when 

 a volume equal to the volume of culture had been added. 



