580 IMMUNITY 



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 sub-cultured 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 conformity 

 with this view Eisenberg and Volk consider that the agglutinat- 

 ing group may be destroyed while the combining group 

 remains, the result being an agglutinoid. 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 inacti- 

 vated by heat or other means, what are known as " zone pheno- 

 mena " occur ; that is, when agglutination occurs with a given 

 dilution of such a serum a lower dilution may fail to agglutinate, 

 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 on 

 the other hand may be well marked when no weakening 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. 



Like immune-bodies, agglutinins are not destroyed at 55 0. 

 (a temperature sufficient to annul bactericidal action), but 

 different agglutinins show variations in this respect, some being 

 affected by a temperature little above that named. The resist- 

 ance to heat also varies when the serum is diluted with salt 



