826 PRECIPITINS AND THEIR APPLICATIONS 



SPECIFICITY 



Although the specificity of reactions of precipitins indicates a similarity to other 

 antibodies, group reactions at low titres or high concentrations of antibody are fre- 

 quent. These may be especially anticipated with low potency sera, with sera which 

 have aged or have been drawn after a prolonged course of immunization. In most 

 cases difficulties in this respect can be avoided by using highly potent antisera, and 

 by carrying out the desired tests at dilutions sufficiently high to eliminate group- or 

 cross-reactions. In routine tests it goes without saying that adequate control mixtures 

 must be arranged in order to gain reliable information from precipitin tests. 



Aside from the detection of protein, the determination of species origin is of con- 

 siderable interest. Group reactions encountered in the precipitin reaction as in other 

 biological reactions have been attributed to close similarity or identity of the various 

 antigens involved, and to close biological relationship of the organic species' furnish- 

 ing the antigens. 



While this may be true to a considerable extent it should not be surprising to en- 

 counter certain protein material several times throughout the animal and plant king- 

 dom when many species are more completely examined. The distribution of so-called 

 "heterophile antigen" indicates that species specificity is not the all-important phase of 

 specificity, and that many overlappings exist in protein distribution which group 

 sometimes very dissimilar and distantly related morphological forms together. This 

 suggests prophylactic immunization with non-toxic varieties of antigens found in dis- 

 ease-producing viruses. ■ 



ORGAN SPECIFICITY 



Aside from species specificity of precipitin reactions, considerable interest at- 

 taches to organ specificity. It is commonly believed that many organs in an animal 

 organism contain one or more precipitinogens more or less common to the species. 

 The detection of these has been regarded as identifying the species. Also it is com- 

 monly believed, and might be anticipated, that certain highly specialized organs such 

 as the eye should contain very similar if not the same material among many species 

 of animals. These substances may be so different from the other antigenic substances 

 of the organism that they may be antigenic (auto-antigenic) when the animal is treat- 

 ed with them. That an animal's own proteins are not generally antigenic for it under 

 normal conditions shows that organ specific antigenic differences are not common. 



PRECIPITIN-PRECIPITINOGEN COMBINATION ifi vivo and in vUro 



On examining the main conditions found in precipitin-precipitinogen reactions 

 there appears a curious apparent coexistence of antigen and antibody in the test tube 

 or the experimental animal. That is, the material or mixture under test reacts with 

 both fresh antigen and fresh antibody .^'^ Why such coexisting antigen and antibody 

 do not precipitate each other is hard to understand. Protective accessory substances 

 may be invoked in order to explain tentatively such an anomaly. It may be recalled, on 



■ Nuttall, G.: Blood Immunity and Blood Relationship. Cambridge University Press, 1904. 



2 Linossier, G., and Lemoine, G.: Compl. rend. Soc. de biol., 54, 85. 1902. 



3 Eisenberg, B.: Bull, de I' Acad, des sc. de Cracow, p. 576, 1902; Cenlralhl.f. Bahteriol., Abt. I, 

 31, 773. 1902. 



