180 CHEMISTRY OF THE IMMUNITY REACTIONS 



The observations of Bond'^ suggest that they may become physically bound to 

 other colloids within the body. 



The structure of the agglutinins (in the Ehrlich theory) is similar to that of the 

 toxin; i. e., there is a haptophore group by which they combine with the aggluti- 

 nogen, and a toxophore group by which they produce the changes that cause agglu- 

 tination. The agglutinogen is probably related to the antitoxins in structure, 

 having a single haptophore to unite with the agglutinin. By degeneration of the 

 toxophorous group of the agglutinin, agghitinoids may be formed. It is believed 

 that agglutinins are cell receptors, which have a group with a chemical affinity 

 for the agglutinogen of the bacterial protoplasm, and also another group which 

 brings about the agglutination. Thej' are, therefore, more complex than the 

 simple receptors that unite with toxins, and are called receptors of the second order. 

 According to Ohno^® the reaction of agglutinin and antigen is in constant propor- 

 tions, and seems to be a chemical rather than a physical reaction. Coplans^^ 

 finds this reaction associated with an increase in conductivitj- in the solutions, but 

 whether this depends upon the agglutinin reaction itself, or upon associated 

 processes, is questionable. 



Agglutinated bacteria can be again separated from one another by the action 

 of organic and inorganic acids, alkalies, acid salts, and bj"- heating to 70'' or 75°. 

 and after once being separated they cannot be reagglutinated by fresh serum. i* 



The Mechanism of Agglutination. — This has been a fruitful 

 field of research, in which the application of physical chemistry has 

 been very profitable. At first it was believed that the clumping was 

 brought about by loss of motility, until it was found that non-motile 

 bacilli were equally affected. Similarly, the hypothesis of adhesion of 

 the fiagellse was disposed of. Gruber^^ and others supposed that a 

 sticky substance, " glabrificin," was absorbed from the serum by the 

 bacilli, which caused them to adhere on contact with one another; 

 but this does not explain the flocking together of non-motile bacilli. 

 Paltauf considered that the specific precipitin (see next section) pro- 

 duced by immunization carried the bacilli down in the precipitate 

 formed, and there is reason to believe that this reaction is of im- 

 portance, but it does not explain all the facts of agglutination, nor is 

 the relation between agglutinating and precipitating power of im- 

 mune serums a constant one. In support of this hj^pothesis is the 

 observation of Scheller^" that mixtures of typhoid bacilli and agglu- 

 tinating serum lose their agglutinability by vigorous shaking, which 

 may be interpreted as the result of disintegration of the agglutinating 

 precipitate. Shaking of either bacteria or serum alone is without' 

 effect. Neisser and Friedemann^^ found that if the bacterial cells were 

 saturated with lead acetate, washed in water until all soluble lead was 

 removed, and then treated with H2S, they were promptly agglutinated 

 and precipitated, supporting other observations that indicate that 

 precipitation within the bacterial cells can lead to agglutination. 

 This sort of agglutination is related to the process of formation of 



"Brit. Med. Jour., June 14, 1919. 

 " Philippine Jour. Sci., 1908 (3), 47. 

 "Jour. Path, and liact., 1912 (17), 130. 

 '8 Eisenberg and V^)lk, Zeit. f. Infektionskr., 1902 (40), 192. 

 "^'8 For comploto bibliography, sec Craw, Jour, of Hygiene, 1905 (5), 113. 

 20 Cent. f. Bakt., 1910 (54). 150. 

 2' Miinch. nied. Wocli., 1904 (51). 4(15 and S27. 



