BI0I.()(JI(;AI> AM) AXTKJKXIC SPKCIl'ICITY 



319 



known and used in l)H('lc'iial identification. That tiiis .si)ecific'ity 

 is definitely due to chemical structure is now generally accepted. 



Thus it will be seen that immunological specificity is but another 

 example of a phenomenon quite common in nature. 



Immunolog'ical Specificity. — CJrubei- and Durham ( 189(5) were 

 really ])ioneers in the study of immunological specificity. They 

 discovered, while working with bacterial antigens, specific and 

 group agglutination. They noted that when they obtained an im- 

 mune serum that agglutinated in high titer suspensions of the 

 organisms used in the antigen, this same immune serum frequently 

 agglutinated closely related bacteria at a lower titer. For example, 

 an antityphoid immune serum that would agglutinate only suspen- 

 sions of E. typJiosa when the serum was diluted 1 : 10,000 might 

 agglutinate suspensions of closely related organisms when diluted 

 to only 1 :100 or 1 :200. 



Fl 



Fig. 14. 



-Durham's conception of the multiplicity of cellular antigens. A, Major 

 antigen. B, C, and D, Minor antigen.^;. 



Durham 's Explanation — Multiple Antigens. — Sometimes 

 group agglutination at a higher dilution could be demonstrated. 

 By using high titered serum they could demonstrate species speci- 

 ficity, but the group reactions did not always indicate closely re- 

 lated species. Durham attempted to explain the group reactions as 

 due to the presence of identical antigens of different amounts in 

 different bacteria. In his opinion, each species of bacteria con- 

 tained a chief antigen that was species specific and a number of 

 minor antigens that might be present in closely related organisms. 

 This concept is indicated in Fig. 14. Here A represents the chief 

 antigenic constituent of the cell while B, C, D, and E represent 

 minor antigens. Any one of these might be found in some other 

 closely related organism in different amounts. Varying amounts 



