VARIATIONS IN TYPHOID BACILLI 313 



These experiments showed that Cohen S cultures did not 

 absorb the agglutinin of any of the three antityphoid sera. 



The work of Bordet has demonstrated the essential importance 

 of electrolytes in agglutination, and the studies of Neisser and 

 Friedemann, Friedberger and others have shown that whereas 

 small traces of salts will flocculate bacteria that have absorbed 

 agglutinin, it requires very large amounts of the same electrolytes 

 to flake out normal (insensitized) organisms. Since the researches 

 of Neisser and Friedemann especially have shown that to a 

 cer+ain extent there is a relationship between the degree of 

 sensitization and the amounts of salt necessary to bring about 

 agglutination, we considered it of interest to determine by com- 

 parative tests the differences in sodium chloride concentration 

 necessary to flake out, on the one hand, the Cohen serum strain, 

 and on the other, the Cohen broth strain after both had been 

 treated with homologous serum. This would show whether or 

 not any trace of agglutinin had been absorbed by the Cohen S 

 strain in the process. 



Tjrphoid bacterial suspensions in Rawling's serum were centri- 

 fuged for thirty minutes and all the supernatant fluid decanted 

 off for another agglutination test; the residue in both centrifuge 

 tubes, one of them containing Cohen S and the other Cohen B 

 strains was poured into a few centimeters of 0.85 per cent salt 

 solution and without centrifuging but after sHght shaking, all 

 the fluid was decanted from the tubes, leaving a mass of bacteria. 

 This was worked into an emulsion by means of a glass rod, and 

 distilled water added drop by drop. The graded dilutions of 

 the 20 per cent sodium chloride were prepared, to range from 

 20 per cent to 0.025 per cent. A half cubic centimeter of each 

 dilution was transferred to small tubes and a half cubic centi- 

 meter of the above bacillary emulsion in distilled water was 

 added to each tube and also to a distilled water control. The 

 results were as follows : 



The percentage shown below is the actual percentage after 

 mixing salt solution and watery bacterial suspension : 



