412 RESEARCH IN PROTOZOOLOGY 



on immunology. Of those in English, particular attention is due 

 Kolmer (1923 and 1928) for technical details; Zinsser (1923) 

 for general discussions; Wells (1925) for the chemical aspects; 

 and the compendium of Jordan and Falk (1928) for a critical dis- 

 cussion of many sj)ecific immunological questions by various 

 authors. For a special consideration of the immunology of the 

 parasites and an extensive bibliography, the reader is referred to 

 a book by the author (1929). 



B. General nature of antigens, test antigens, antibodies and\ 

 serological reactions. The parenteral introduction of a large class 

 of substances, termed antigens, into an animal is followed after 

 a lapse of time by the appearance of antibodies in the animal's 

 serum which in turn will react specifically, not only with their 

 specific antigens but with certain derivatives of them in in vitro 

 tests. In order to include all the substances which will react with 

 antibodies in the serological tests and to differentiate them from 

 true antigens, the term ''test antigen" has been used in the present 

 review. More explicitly, substances to be antigens, i.e., stimulate 

 the production of specific antibodies in an animal, must be in 

 colloidal solution, must be foreign to the test animal, must pene- 

 trate beyond the epithelial surfaces which protect the body, most 

 probably must be protein (Wells, 1925), and may be infecting 

 organisms or their derivatives (including toxins) or an inex- 

 haustible number of proteins, such as ^gg albumen, blood, etc. 

 Substances to be test antigens, on the other hand, i.e., able to 

 react specifically with serums of animals in which the antibodies 

 occur as a result of immunization or infection, may be protein, but 

 are not necessarily so. Thus, in some cases, they are identical 

 with the true antigens and are protein, as when highly purified 

 proteins, such as ^gg albumen, are used. In other cases, complex 

 carbohydrates (Zinsser's "residue antigens," Avery and Heidel- 

 berger's "specific soluble substances") or lipoids (Landsteiner's 

 "haptenes") stimulate the production of antibodies only if they 

 are in comljination with proteins, but later, can react by them- 

 selves specifically with the resulting antibodies and with even 

 more precision than the corresponding proteins alone. 



Tremendous strides have been made toward an exact chemical 

 understanding of the nature of antigens and test antigens, but 

 little so far is known of the nature of antibodies. They have 

 not been isolated chemically, but are known as properties of 



