PROPERTIES OF THE BACTERIOPHAGE 287 



temperature, it is possible to recover the bacteriophage, still virulent, 

 from the few drops of syrupy liquid remaining in the bottom of the 

 tube.^'' The fluid may, indeed, be evaporated to dr^ess, particularly 

 in the apparatus which I have described, and in the pulverized residue 

 virulent corpuscles may still be found. 



3. FLOCCULATION OF CORPUSCLES 



The bacteriophage corpuscle being, from the physical point of view, 

 a colloidal "micella" it should possess an electric charge, and in order 

 to determine the sign of this charge it is only necessary to ascertain 

 whether these micellae are flocculated by H+ or 0H~ ions. In the first 

 case the charge would be negative, in the second it would be positive.* 



We know that the bacteriophage usuaUy multipHes in an alkahne 

 medium, and that for the overwhelming majority of races, the cor- 

 puscles remain inactive in an acid medium. Furthermore, as da Costa 

 Cruz has shown by direct experiment, the corpuscles flocculate under 

 the influence of acids. 



This being the case the corpuscle possesses a negative charge, and 

 consequently the bacteriophage is what is termed a "negative-colloid." 

 Incidentally, we may add that according to many investigations the 

 great majority of bacteria also possess a negative charge, and they also 

 are flocculated by acids. 



But we have seen that certain races of the bacteriophage may bring 

 about bacteriophagy in an acid medium (Asheshov^^-^s). Da Costa 

 Cruz has isolated a race of the bacteriophage which is active in a medium 

 with a pH of 5.1, that is, in a medium definitely acid. It would appear 

 then, that flocculation by acid does not take place at the same pH for all 

 races. 



Maisin^29 ^^g found that the corpuscles are completely precipitated 

 by saturation with ammonium sulfate and that they may be recovered, 

 stiU virulent, from the precipitate. Precipitation is only partial with 

 half saturation with the sulfate. Magnesium sulfate acts in the same 

 way (de Poorter and Maisin^^)^ jjere again the corpuscles react like 

 "protein miceUae." 



Levaditi and Nicolau^'^^ have seen that the virus of vaccinia behaves 

 in the same way when subjected to these conditions. 



Bacteriophage corpuscles are carried down only in part by the pre- 

 cipitate formed with tricalcium phosphate (Maisin*^^), and I have shown 

 that there is but Httle removal of the corpuscles by the precipitate of 



* Sender and Picton, Hardy, J. Perrin, etc. 



