AGGLUTININS AND PRECIPITINS 95 



Furthermore, they offer a protocol showing the similarity be- 

 tween the reaction of colloidal iron hydroxide upon mastic emul- 

 sions and the agglutination phenomenon in reference to inhibition 

 zones. It will be seen that stronger concentrations of the iron 

 hydroxide fail to precipitate, thus simulating the action of strong 

 concentrations of an agglutinating serum of high titer or of an old 

 serum. The protocol follows: 



Colloidal iron hydroxide Mastic emulsion 

 1.0 I.O C.C. 



0.5 i.o c.c. 



0.25 i.o c.c. 



O.I I.O C.C. 



0.5 i.o c.c. 



O.02S 2.O C.C. 



O.OI I.O C.C. 



0.005 i.o c.c. 



0.0025 i.o c.c. 



O.OOI I.O C.C. 



This latter protocol is of significance not only in relation to 

 agglutination, but is of importance also in connection with the 

 Neisser-Wechsberg phenomenon of complement-deviation (not 

 fixation) discussed in connection with bacteriolysis. As Zinsser says, 

 " it seems to be a universal fact governing the union of colloidal 

 substances, that definite quantitative proportions must be main- 

 tained in order to lead to reaction, this being, possibly, explicable on 

 the basis that actual union can take place only after disturbance of 

 the electrical balance which keeps the particles apart." The assump- 

 tion that agglutinoids have an important bearing on the presence of 

 inhibition zones is not necessary if we accept the colloidal nature of 

 agglutination. This does not entirely controvert the existence of 

 altered agglutinin with a binding power for agglutinogen. 



Not only may salt-free bacteria-agglutinin combinations be 

 agglutinated by salts but, as Friedberger has shown, certain organic 

 substances, such as dextrose and asparagin, serve also to produce 

 agglutination in such salt-free mixtures. These substances do not 

 dissociate in solution as do salts, and therefore produce no electric 

 phenomena. This fact presents a certain objection to the final 

 acceptance of the colloidal theory of agglutination, but it is possible 

 that the mechanism in this instance is of a nature different from 

 that of the immunological process, and certainly the great mass of 

 evidence is in favor of the reaction of agglutination being of 

 colloidal nature. 



Nothing has been definitely brought forward in the physico- 

 chemical examination of agglutination to explain specificity, except 

 the fact previously indicated, that variations of hydrogen ion con- 

 centration have a relatively specific action on bacteria. As is 

 known, the definite identification of bacteria by this method has 

 not been satisfactory. The specificity of immune serum agglutina- 



