66 THE FLOCCULATION OF BACTERIA, 



of clay. If they behave like suspended particles, fiocculation 

 may be utilised as a means of obtaining them more readily from 

 the solutions in which they have been grown. But better than 

 this, fiocculation as in pseudo-solution might be the means of 

 separating those bacteria which are supposed to be ultra-micro- 

 scopical — as, for example, the organism of pleuro-pneumonia 

 (Nocard and Roux), which is hardly visible under the highest 

 powers of the microscope. It might also lead to the elucidation 

 of some questions connected with the agglutination of bacteria 

 by active sera. 



With regard to the choice of flocculating agents, it must be 

 borne in mind that salts of the heavy metals would coagulate the 

 constituents of the culture media and of the organism. We are, 

 therefore, deprived of the strongest agents. The salts of the 

 zinc and iron metals are too prone to form basic salts, and 

 accordingly a choice of the metals of the alkalies and alkaline 

 earths remain. Of these metals, calcium has the highest floccu- 

 lating power, and, therefore, calcium chloride was employed in 

 my experiments. The density of bacteria as shown by Almcpiist 

 is about 1'4, and that of most inorganic particles much more — 

 say from 1*8 to 2-6; it was, therefore, to be expected that a strong 

 flocculating agent would be required. 



Preliminary experiments showed that a fiocculation was obtained 

 with calcium chloride, and also indicated what should be the 

 approximate strength of the flocculating solution. At first a 

 meat-extract, neutralised with sodium hydrate to phenolphthalein, 

 and at a later period meat bouillon, neutralised in the same way,, 

 were used for growing the cultures. The organisms which I 

 regarded as being typical for the purpose were Bad. prodigiosum, 

 Bad. coli commune, and Bad. typhi. A solution of calcium 

 chloride crystals was prepared of such strength that a litre con- 

 tained the molecular weight expressed in grams, i.e., the solution 

 contained 40 grams of calcium per litre. Dilutions of this were 

 made in ratios of ~ u , -^ T , and J^. The precipitation of the 

 cultures was conducted in small test-tubes, into which were 

 pipetted 2 c.c. of the cultures which had generally grown for two 

 days at 30° C, and had been passed through a cotton-wool plug 

 to eliminate clumps. The quantities of the flocculating agents 

 that were added varied general!}' from 0-2 to 10 c.c. I may 



