580 IMMUNITY 



showed that if the clumps of agglutinated bacteria are freed from 

 salt by washing in distilled water they become resolved, and that 

 on the addition of some sodium chloride they are formed again, 

 and Joos has also brought forward striking confirmatory evidence 

 as to the necessity for the presence of salts. It is thus evident 

 that in the phenomenon of agglutination more than one factor 

 is concerned, and it is possible that in part it may depend on 

 some change in the molecular relationship of the bacteria to 

 the surrounding fluid, analogous to altered surface tension. 



In the phenomenon of agglutination we have to distinguish 

 two factors, namely, the combination of agglutinin and agglu- 

 tinable substance (agglutinogen) and the actual clumping of the 

 bacteria, and it is to be noted that whether or not the latter 

 event follows depends on the physical condition of each of the 

 two substances concerned. For example, in some cases when 

 the bacteria are heated at a temperature of 65° C, for some time, 

 they may lose the faculty of being agglutinated while they may 

 still retain the property of combining with or binding agglutinin. 

 Dreyer and Jex Blake have observed the remarkable fact 

 that in certain instances on being heated to a still higher 

 temperature they may once more become agglutinable. Another 

 point of practical importance is that bacteria when freshly grown 

 from the tissues are very often less agglutinable than they after- 

 wards become when subcultured for some time. 



As stated above, the agglutinins are usually placed in the second order 

 of anti-substances, and are regarded as possessing a combining group and 

 an active or agglutinating group. The constitution would thus be 

 analogous to that of a toxin, and in comformity with this view Eisenberg 

 and Volk consider that the agglutinating group may be destroyed while 

 the combining group remains, the result being an agglutirurid. The 

 evidence for this lies in the fact that when an agglutinating serum is 

 heated to a certain temperature, not only does it lose its agglutinating 

 action, but when the bacteria are treated with such a serum, their 

 agglutination by active serum is interfered with, a sort of plugging up of 

 the combining molecules having apparently taken place. Again, with 

 agglutinating sera partially inactivated by heat or other means, what are 

 known as " zone phenomena" occur ; that is, when agglutination occurs 

 with a given dilution of such a serum a lower dilution may fail to ag- 

 glutinate, and this they suppose to be due to the interference of the union 

 of agglutinin by agglutinoid in the greater concentration of serum. On 

 the other hand, there are facts which cannot be brought into harmony 

 with this view. For example, Dreyer and Jex Blake have shown that 

 the inhibition zone may be slight when there has been much destruction 

 of agglutinin, and en theother hand may be well marked when no weaken- 

 ing of the agglutinating power has resulted from the heating. The 

 physical changes underlying such phenomena are. still very obscure, but 

 we may say at present that the existence of agglutinoids has not yet been 

 proved. 



