ORGAN (TISSUE) DIFFERENTIALS 533 



precipitation method, especially in combination with specific absorption, has 

 been used most commonly in the analysis of such antigens. 



(2) If the immune serum directed against a certain organ, or against a 

 characteristic substance derived from this organ, reacts with the analogous 

 organ or substance not only from the species which served as the donor of 

 the antigen, but also from other species more nearly related to or even 

 farther distant from the donor species, then we assume that these immune sera 

 and the corresponding antigens are organ-specific. Thus, as stated, the immune 

 serum directed against the lens of mammals may react about equally well 

 with lens material from birds, reptiles and amphibia, and even, although not 

 quite so well, with lens substance of fishes ; in this case we have therefore 

 predominantly to deal with organ differentials. 



(3) If the immune serum, directed against a certain organ, should react 

 also with blood serum or some of its constituents, or with other organs of 

 the donor species, the latter reaction must at least be weaker than the one 

 which takes place with the organ which served as antigen for the immune 

 serum. In some cases the reactions are graded in accordance with the 

 graded relationships obtaining between the antigen-furnishing organ or 

 tissue and the other organs or tissues 'of the donor species. Thus immune 

 serum against guinea pig erythrocytes may react not only with erythrocytes, 

 but also with leucocytes and spleen tissue of the guinea pig, but not with 

 other organs of the guinea pig, nor with the corresponding rat cells; and 

 the immune serum against brain may react also with testis, but not with 

 other organs. If an immune serum reacts not only with constituents of an 

 organ which served as antigen but also with a certain constituent of the 

 blood, it does not necessarily mean, therefore, that an organismal differential 

 served as antigen — although it may have this meaning — but it may mean in 

 some instances that the splitting of very complex material, characteristic of 

 an organ, into somewhat more elementary substances may lead to a relative 

 organ-specificity, which allows for the presence of similar substances in 

 certain other organs or tissues, or in the blood of the same species. The 

 chemical constituent common to two or more organs and, perhaps, to blood, 

 which is responsible for the joint reaction of these organs or of the blood with 

 the immune serum primarily directed against one particular organ, would not, 

 in this case, be a part of the organismal (species) differential, but of the 

 differential of the organ used for immunization, as well as of the differentials 

 of certain other organs or tissues. 



It is possible in some cases to increase the specificity of the immune serum 

 against an organ differential and to diminish or destroy entirely its reaction 

 with organismal differentials by boiling the antigen before injecting it. In 

 this way the organismal differentials, which concomitantly with the organ 

 differentials might serve as antigens, are injured in their antigenic power to 

 a much higher degree than are the organ differentials. Furthermore, if the 

 test reaction is carried out with an alcohol extract of the organ which served 

 as antigen, instead of with native or boiled antigen, the organ-specificity is 



