THE CHEMICAL NATURE OF DIFFERENTIALS 571 



bodies produced in rabbits by injection with the glucuronic acid antigen 

 protects mice against infection with Type II pneumococci ; the antiserum 

 with the galacturonic acid antigen is ineffective. Furthermore, the immune 

 serum of rabbits injected with p-aminobenzyl (1 cellobiuronide confers passive 

 immunity in Types III and VIII pneumococcal infection, whereas the serum 

 of rabbits immunized with p-aminobenzyl (S gentiobiuronide is inactive. But 

 both immune sera against cellobiuronic acid and gentiobiuronic acid provide 

 passive immunity against Type II pneumococcus infection. If the glucuronic 

 acids are removed from the antigens, no protection is obtained against Type 

 II pneumococcus. It may therefore be concluded that in the latter case the 

 two glucuronic acids are the active constituents of the antigen. On the other 

 hand, immunity against Types III and VIII pneumococcal infection depends 

 upon the particular union between the two constituents of the two disac- 

 charides, cellobiuronide and gentiobiuronide, one kind of union being effective 

 while the other is ineffective. 



Not only have relatively simple organic substances, joined to protein by 

 means of diazotization, served as haptens, but also alcohol extracts of various 

 cells and organs which, in combination with protein, function as antigens and 

 call forth the production of antibodies. In this way, Forssman heterogenetic 

 antigens, blood-group antigens, especially the antigen for blood group A, and 

 organ-specific antigens have been used. The latter have been prepared also 

 from boiled organs. In general, these alcohol soluble haptens are heat stable. 

 They function as complete antigens and call forth the production of anti- 

 bodies in combination with protein, especially the protein of a heterogenous 

 blood serum. At first it was assumed that the haptens in these alcohol extracts 

 were lipids, but subsequent investigations made their lipid nature doubtful 

 in many instances. In accordance with the work of Landsteiner and Levene, 

 it is now assumed that the Forssman hapten is a combination of a carbo- 

 hydrate and a lipid, and it is furthermore assumed that a carbohydrate may 

 be present also in the blood-group antigen. As to the organ antigens, they 

 may be proteins, in which, however, other groups are active than those which 

 represent the organismal and especially the individuality differentials. The 

 active organ differential groups are heat stable. Some organ and "substance" 

 antigens are conjugated proteins or combinations between haptens and 

 proteins. 



In regard to the organismal differentials, especially the individuality and 

 species differentials, these depend essentially on certain characteristic proper- 

 ties of proteins, which the various parts of an individual, or the individuals 

 composing a species, have in common. In the beginning of this chapter we 

 have already discussed some of the properties of cell and tissue proteins and 

 have mentioned the fact that the individuality differential is lost whenever 

 the proteins are denatured. We have furthermore stated that the process of 

 denaturation may depend primarily on a breaking of linkages between certain 

 sidegroups in parallel peptid chains or in the same peptid chain coiled upon 

 itself, and such a breaking of linkages must therefore destroy the individ- 

 uality differential ; or it may depend upon a process of uncoiling. This does 



