No. 642] SEROLOGICAL REACTIONS 



respective of whether the antigen consists of bacteria or 

 of other protein materials, there is a gradational spe- 

 cificity of reactions which apparently corresponds to tax- 

 onomic relationships. 



An even more delicate biochemical measure of kin^^liip 

 than the known immunological reactions has apparently 

 been established through the extensive researches of 

 Leo Loeb^ and his associates on transplanted tissues. In 

 numerous of his papers Loeb has called attention to the 

 remarkable power of transplanted tissues to indicate dif- 

 ferent degrees of even close individual relationship, such 

 as the individual to itself, to a brother or sister, to a 

 parent, to a more distantly related individual of the same 

 species, or to an individual of a different species. Par- 

 ticularly the lymphocytes of the host serve as a delicate 

 indicator of such relationships. 



Loeb assumes that a specific chemical group which he 

 designates as individiiolity-differential is common to all 

 the tissues of an individual and that in virtue of this 

 characteristic each creature differs from the others of the 

 same species. The individuality-differential of a trans- 

 plant (except in autotransplantation), since it is not 

 ada])ted to its new environment, assumes iniurious prop- 

 erties, ])ro]")ably ])y engendering toxins. The relative 

 strengths of tliose are (let(M-mined by iho dciri-oe of rela- 

 tionship thai r\;<tv between the seiiive of the ti-a!i-| 'h-mt 

 and the host, in the eiivulatiim' tlni.l> ef a -iveii indi- 

 vidual, he believe^ that theiv are antn^nI-Maiirr. " 

 which exercise importatit n^u'Hhui\'e t'lnict ions >iieh. for 

 example, as keeping the \-ascnh-ii' -u]>i>I\- of the Narious 

 tissues at an o])timum, or lu>l<liim- in <'heek lyni|>hoe\ tes 

 and invasive fibroblasts which wlien ina(le(|uate]\ re- 

 strained, as in old age, become ( lest met i\ e ;ii:-eiits. In 

 one place ho speaks of their >t iiniHat inu- eftVets and lie 

 regards them as responsible direct l\ oi- indirectlx for the 

 marked vascular reaction call('<l fortli by antot ransplants. 



In sexual reproduction, obviously tu(» ditTerent " indi- 

 viduality-differentials " must eonibi?i(' to foiiu the new 



tennediaey cont' 



imlividualitv-diff.'i 

 fuuh. are of Nar.Ni 



* Amer. Xat., LIV, 



