BIOLOGICAL AND ANTIGENIC SPECIFICITY 323 



crystalline lens of the eye and of the testis are possessed by all 

 species, while Forssman's antigen and somewhat similar sub- 

 stances recently described by Landsteiner and Levine (1932) are 

 peculiar to only a limited number of species of animals as well 

 as a few species of bacteria. Since Forssman's antigen is a lipoid- 

 carbohydrate-protein complex, or at any rate a hapten-protein com- 

 bination, it is possi])le that the hapten portion is the fraction com- 

 mon to different species, etc. In regard to lens protein, Kraus, 

 Doerr and Sohma (1908). Uhlenhuth (1910), Hektoen (1921, 

 1927) have found tliat ])rotein from the crystalline lens of the 

 eye is antigenically and cliemically the same in all species. It even 

 functions as an antigen when injected into the same species. Von 

 Dungern and Hirschfeld (1910) claim to have demonstrated 

 similar nonspecies specificity for testicular protein, although they 

 did not find such marked organ specificity as exists in the case of 

 lens protein. 



Keratin, Mucin, Etc., Lack Species Specificity. — AVells (1929) 

 says that "it is altogether reasonable that lens proteins, keratin, 

 mucin and other proteins whose function is not metabolism, should 

 be nonspecific. Each of these proteins has quite the same function 

 to perform in every species, and is set off from the active tissues to 

 perform it." 



Thyroglobulin.— Hektoen and Scliulliof (1923) found that 

 thyroglobulin is antigenically different from the other proteins of 

 the same animal from which it is obtained but antigenically similar 

 to thyroglobulin of other species. 



Milk Proteins. — Proteins of normal body secretions. Milk is 

 a normal secretion of the mammary gland and contains proteins, 

 carbohydrates, fats, and other ingredients. Casein, the principal 

 protein, is chemically identical and antigenically similar for all 

 species, but in each species its chemical and antigenic properties 

 are different from other body proteins. On the other hand, the 

 globulin present in milk is chemically and antigenically similar 

 to the serum globulins of the s])ecies and shows the same .species 

 specificity as the .serum globulins. 



Antigenic Components of the Egg.— Wells (1911) and Hek- 

 toen and Cole (1928) have demonstrated five antigenic components 



