ORGAN (TISSUE) DIFFERENTIALS 547 



differential. Thus homoiogenous lens material does not commonly produce 

 antibodies against lens, but Hektoen and Schulhof found that it may do so 

 if the rabbit which is to be immunized by means of homoiogenous lens, has 

 on a previous occasion been sensitized against heterogenous lens. Otherwise, 

 if homoiogenous lens does elicit formation of immune substances, these are 

 very weak; this seems to be true also of spleen. Similarly, it is as a rule 

 necessary to use heterogenous brain in order to produce organ-specific anti- 

 bodies against this tissue ; a heterogenous carrier must be combined with 

 alcohol extracts of lens or brain to produce immunization. On the other hand, 

 according to Kato, rabbit fibrinogen may elicit in rabbits which are injected 

 with it, the formation of antibodies against this antigen, although it possesses 

 the same organismal differential. 



Likewise in the case of organ globulins, including thyreoglobulin, homoiog- 

 enous immunization seems to succeed, perhaps because these globulins do not 

 occur normally in a free state in the various organs but are bound to other 

 substances, and if they are freed from the latter, they are strange to the 

 organism which is not adapted to their effects. In the case of spermatozoa, it 

 seems that even autogenous cells may serve as antigen, and the same has been 

 claimed for the lens of the eye and for the skin by some authors, but this has 

 been contradicted by the findings of others. It is conceivable that organ 

 differentials may perhaps act as autogenous antigens under certain conditions, 

 although the organismal differentials cannot act as such. The organism and 

 all its parts are adapted to the autogenous organismal differential because it 

 is present in all, or almost all, the organs of the body, whereas each organ 

 differential is limited to a certain restricted area and is therefore strange to 

 other areas. There may be also some other variations in the reactions of 

 different organ differentials. Thus if once the antiserum has been produced, 

 it may react in vitro even with antigens of a homoiogenous nature, at least 

 in the case of lens and brain ; but as far as antiserum against fibrinogen is 

 concerned, a reaction seems to take place more intensely with heterogenous 

 than with homoiogenous substances. 



In regard to the chemical character of the organ differentials, it appears 

 that different types of substances may be involved. We have seen that 

 thyreoglobulin as well as globulins from other organs may serve as organ- 

 specific antigens. Similarly, fibrinogen, serum-globulin and hemoglobin possess 

 a substance (or organ) specificity in addition to species specificity. In the 

 lens Hektoen and Schulhof have shown that the two crystallins, which are 

 of protein character, as well as the whole lens can serve as organ-specific 

 antigens. In brain and epiphysis organ differentials, which also are pre- 

 sumably proteins, have been demonstrated. We may then conclude on the 

 basis of these immunological findings that organ differentials may be of a 

 protein nature. But there are some other data which indicate that also sub- 

 stances of a different kind may thus function. In lens, brain, carcinomatous 

 tissue, and also in leucocytes, substances which seem to represent organ 

 differentials can be obtained by means of alcohol extraction. Such alcohol 

 soluble extracts may react in a specific manner directly with the antibodies, 



