HTOLOdlCAL AND ANTIGKXK" SI'KCIFICITV 321 



COCCUS, and since then Dochez, Aveiy, Blake and others have 

 found, by means of aiLiglutination, antigenic types for the meningo- 

 coccus, streptococcus and man}- other kinds of bacteria. Thus it 

 will be seen that at least two kinds of specificity can be demon- 

 strated by immune reactions, one that applies to species and the 

 second to type variation within a species. 



Serum Proteins vs. Cellular Antigens. — Landsteiner (1928) 

 has called attention to the fact that species relationships are indi- 

 cated by a study of the serum proteins, while type differentiation 

 within a species is determined by studies of the cellular antigens 

 peculiar to the species. Wells (1929) considers that even the 

 serum proteins show two kinds of specificity and this is borne out 

 hy the work of Nuttall and others. 



Ehrlich (1910) says that his side chain theory of immunity 

 implied that antigenic specificity was dependent upon the chemi- 

 cal constitution of the antigen. Subsequent research has ap- 

 parently confirmed this concept. 



Formerly it was thought that only complete proteins were 

 antigenic but it is now agreed that a few bacterial polysaccharides 

 (e.g., Type I pneumococcus) and perhaps a few lipid-carbohydrate 

 complexes may stimulate specific antibody formation. Wells 

 (1929) summarized the properties of antigenic protein substances 

 somewhat as follows : 



Properties of an Antigen. — They are all complete proteins in 

 a colloidal state, soluble in the fluids of the animal body and 

 possessing a necessary number and kind of aromatic amino-acids. 

 To elicit antibody production they must be introduced beneath 

 the "epithelial coverings of the body," i.e., into the tissues of an 

 animal not possessing similar antigens in its body proteins. (It is 

 now generally believed that many of these properties are possessed 

 by all antigens whether protein or carbohydrate.) 



To appreciate the basis for the above conclusion of Wells and 

 others, it is necessary to compare the results of chemical and 

 immunological investigations of both animal and plant proteins 

 as well as experimentally modified proteins. Similar comparisons 

 should also be made for the carbohydrates and lipoids. 



Animal Proteins. — Proteins of the animal body consist of the 

 proteins ol' tlie l)lood, tissues, and normal secretions of the body. 



