500 STUDIES IN IMMUNITY. 



molecule of the antibody rather than in one of the antigen. The 

 hypothesis of a functional group in the molecule of the agglutinin 

 is all the more doubtful inasmuch as it is not the only substance 

 which can render bacteria sensitive to the flocculating action of 

 salts. Bacteria that have absorbed iron, uranium, or aluminium 

 compounds are subsequently flocculableby salts (Neisser and Friede- 

 mann, Bechhold, Gengou) ; silicic acid is similar in its action (Land- 

 steiner and Jagic). 



It has been found that agglutinins when heated may keep the 

 property of uniting with bacteria although they lose the property 

 of agglutinating them (Michaelis, Eisenberg and Volk, Bail). And 

 to explain this fact it has been said that under these conditions the 

 agglutinin loses its agglutinating group but keeps its combining 

 group.* Certain bacteria act in the same way as agglutinins. The 

 typhoid bacillus, when heated to 80 degrees, still fixes agglutinin but 

 is not agglutinable (Weil).t An aqueous solution of agar, so diluted 

 as to be only slightly viscuous at room temperature, agglutinates 

 barium sulphate suspended in water. Heating such a solution 

 destroys this property without affecting the adsorbing property: 

 under these conditions it produces the opposite effect, namely, dis- 

 seminates the particles of barium and gives a milky appearance to 

 the fluid (Gengou). Can we say here that by heating this solution 

 we have caused it to lose its agglutinating molecular group? As 

 Forges has already stated, the hypothesis of the existence of such a 

 group in the antibody molecule, has no foundation; he found on 

 studying the effect of heat on the agglutinating power of the albu- 

 minous substances of serum for mastic emulsions, that he could 

 obtain entirely similar results to those that have been noted for 

 agglutinins and bacteria. { Any change in the physical properties 

 of the constituents of the complex, agglutinin-bacterium, and par- 

 ticularly as regards the degree of colloidal stability, may influence 

 the state of equilibrium of this complex in respect to the surround- 

 ing fluid, and on this state of equilibrium the phenomenon of agglu- 



* It is well known that precipitins give similar results (Kraus and von Pirquet) . 



f This same author has shown that B. typhosus, which under normal condi- 

 tions isfeebly agglutinated by gelatin, loses this property when heated to SOdegrees. 



t Neisser and Friedemann and Bechhold have contributed interesting results 

 on the effect of gelatin, serum and the like, on the agglutination of mastic by 

 electrolytes. 



