COLLOIDAL THEORY OF ANTIBODIES 323 



action of agglutinin or bacteria. Here also the solid particles may 

 take up much more antibody than is necessary for agglutination 

 to be induced if the serum be added all at once. It may be pointed 

 out that this has a practical value in the estimation of the degree 

 of agglutinating action as determined by the degree of dilution in 

 which the action will take place. It is not proper to make a strong 

 dilution of the serum in the bacterial emulsion, and to dilute this 

 with further amounts of the latter, unless the subsequent dilutions 

 are made quickly. Otherwise, all the agglutinin may be removed 

 by the bacilli in the first dilutions, and those subsequently added 

 be apparently unaltered. The most accurate method is to prepare 

 all the serum dilutions required of double strength, and to add to 

 each an equal volume of bacterial emulsion. On the other hand, 

 when a bacterial emulsion is added to a serum in successive doses, 

 more agglutinin is taken up than when the whole amount is added 

 at once. 



Next as regards the phenomena in which an excess of antibody 

 has apparently a reversing action, the best-known examples of 

 which are : (i) the deviation of complement, or Neisser-Wechsberg 

 phenomenon ; (2) the presence of zones of inhibition in which no 

 precipitation occurs in mixtures of serum and precipitin ; and 

 (3) the similar phenomena observable in the agglutinins. All 

 these have been discussed previously and explanations suggested. 

 These explanations have the merit of not involving any pheno- 

 mena of nature different to those familiar in immunity reactions, 

 but there are objections to all. Thus, Neisser and Wechsberg's 

 explanation of the deviation of complement would have us believe 

 that uncombined complement has a greater affinity for alexin than 

 that which has had its cytophile groups combined with cell re- 

 ceptors a phenomenon exactly opposite to that which occurs in 

 * haemolysis, where the process can be studied with greater accuracy. 

 We have also seen difficulties in the way of accepting Gay's 

 explanation, the full particulars of which are not yet available. 

 In the same way the inhibiting effects of large doses of precipi- 

 tating or agglutinating serum may apparently be explained on the 

 hypothesis of the existence of precipitoids and agglutinoids of 

 higher combining affinity than their unaltered antibodies, but it is 

 at least doubtful whether this is entirely satisfactory. It is difficult 

 to believe that the effect of moderate heat is to increase the com- 

 bining affinity of the agglutinin, whereas greater heat destroys it 

 entirely, and it is altogether different to what is observed in the 



21 2 



