210 IMMUNOLOGY 



Bordet's Definition. — This led Bordet* to adopt the followmg 

 definition for agglutination, "It is the union into masses of or- 

 ganized scattered particles by some peculiar influence that changes 

 the properties of molecular adhesion." "The agglutination of 

 bacteria is due to a change in molecular adhesion between the 

 l)odies of the bacilli and the surrounding fluid.." 



Bordet's Experbients on Effect of Electrolytes on Chol- 

 era Vibrios. — At that time it was apparently well known tliat clay 

 forms a fine, homogeneous emulsion in distilled water, but that 

 agglutination and rapid precipitation of the particles occurs when 

 a small amount of sodium chloride is added. This suggested an 

 experimental approach to the study of bacterial agglutination. 

 Bordet made a suspension in salt solution using 24-liour-old 

 cultures of Microspira comma and 10 c.c. of saline to each culture. 

 To this homogeneous suspension he added sufficient anticholera- 

 immune serum 1o produce complete agglutination of the bacteria. 

 He then centrifuged and decanted the supernatant fluid and 

 resuspended the sediment in enough distilled water to make a 

 rather thick emulsion. This lie added to two test tubes in equal 

 amounts. To tube No. 1, he added distilled water and to tube 

 No. 2, physiological saline. These tubes were then shaken and 

 centrifuged and resuspended as before, i.e., the sediment of tube 1 

 in distilled water and of tube 2 in saline. The tubes were then 

 shaken and allowed to stand. Bordet says, "It is found that 

 clumps form rapidly in llio tube containing salt solution, ])ut that 

 the bacteria renuiin indefinitely in suspension in the tube contain- 

 ing distilled Avater. " He also removed some of Ihc distilled water 

 emulsion and added a small amount of sodium chloride and ob- 

 tained rapid agglutination. 



Bordet thiLs concluded lliat the first phase was a specific ad- 

 sorption of antibody (agglutinin) by the antigen (bacteria) and 

 that the second j^hase was one of agglutination in which the sen- 

 sitized cells were clumped upon the addition of electrolytes. It 

 should be noted that the anti])ody was not removed by washing in 

 either distilled water or salt solution. For a brief discussion of 

 the physical chemical concepts involved in flocculation, the student 

 is referred to the disciLssion of colloids included in the appendix. 



♦Reprinted by permission from Bordet and Gay'.s Stivdies in Imimmity, 

 published by John Wiley & Sons, Inc. 



