t)6 THE FLOCCULATION OF BACTERIA, 



coli commune. The bacteria were thoroughly precipitated, and 

 presented similar appearances with the following amounts of 

 calcium in milligrams per 100 c.c. of total suspension (marked 

 with a f in the table). 



Bad. typhi ... ... ... ... 23 



,, prodigiosum . . . ... ... ... 92 



„ coli commune ... ... ... 114 



A proportion roughly as 1 : 4 : 5. 



Bearing in mind the utility of being able to separate the 

 organisms quickly by nitration through paper, I filtered the 

 cultures through paper of fine texture like that used for fine 

 precipitates such as barium sulphate. To avoid the possible 

 passage of the bacteria over the inside and down the outside of 

 the filter, the margin of the paper was painted with vaseline. 

 The smallest quantities of calcium necessary to give a clear filtrate 

 were as follows (marked with a * in table) : — 



Bad. typhi ... ... .. ... 18 



., prodigiosum... ... ... ... 67 



„ coli commune ... ... ... 92 



A proportion again roughly as 1 : 4 : 5. 



With the object of ascertaining whether or not the bacteria 

 were retained on the filter paper, the Bad. prodigiosum precipi- 

 tate was washed on the filter, five times, successively with dilute 

 calcium chloride, using 2 c.c. portions of T ^ gram-molecule per 

 litre solution. The number of bacteria were determined in a 

 large loop of the successive washings by means of plate cultures. 

 The filtrate contained many bacteria; the fourth washing grew 

 two colonies, and the fifth washing was sterile. The bacteria 

 that were precipitated had been retained upon the filter paper. 

 It is, therefore, shown that practically complete coagulation of a 

 meat or bouillon culture can be obtained in an hour by the 

 addition of 06 c.c. —^ gram-molecule per litre solution of 

 calcium chloride to 2 c.c, or 0-66 grams of crystalline calcium 

 chloride to 100 c.c. of culture. This applies to these three 

 experimental bacteria, and probably to all the others. 



