PROTEID PRECIPITIN SPECIFICITY 1 29 



The result should be read after twenty minutes at room temperature. 

 As a further control a similar row of tubes should be made with the extract 

 of the non-bloody part of the clothing in order to show that the latter 

 alone does not give the reaction. 



Even putrid or otherwise chemically changed proteids may still give 

 the precipitin reaction. 



The precipitation test only determines the animal species from which 

 the proteid originates, but cannot prove whether it comes from the blood, 

 semen, milk or other proteid body. In order therefore- to make a medico- 

 legal diagnosis of " human blood stains," chemical evidences 

 "Origin" must in addition be brought forward, that the stain really 

 and "Con- consists of blood. Obermeyer and Pick have further shown 

 stitutional" that fcesides animal specificity (" origin specificity"), pre- 

 Specificity. dpitation a l so demonstrates the " constitutional specificity " 

 of proteids. 



If instead of employing pure animal or plant proleids for the 

 immunization of animals, variously changed albumins are used (heated 

 albumins, acid albumins, formaldehyde albumin, etc.) the organism reacts by 

 producing antibodies of a characteristic nature, different from those de- 

 veloped after inoculation with the pure albumin. For example, the serum 

 of a rabbit imm unized for a long time with horse's serum (normal immune pre- 

 cipitin) will produce a precipitate when mixed in vitro with the pure horse's 

 serum and not when added to the latter, heated, even if the normal 

 immune serum is of very high titer. On the other hand, if a rabbit is 

 injected with horse's serum which has been changed by being diluted and 

 boiled for a short time, the immune serum thus obtained will react not only 

 with normal horse's serum but also with heated serum and a group of its 

 decomposition products with which the normal immune serum ordinarily 

 never induces a precipitate. 



This fact is of practical application. In meat substitution, it is very popular to boil 

 the sausage in order to make detection of the substituted meats more difficult. With 

 the aid, however, of precipitins produced by immunization with heated proteids, this 

 fabrication is more easily detected than if a normal immune serum were used. 



While animal specificity is not destroyed when the albumins are 

 modified in the above manner or changed by tryptic digestion or oxida- 

 tion, Obermeyer and Pick have demonstrated that their specificity is 

 lost when an iodin, nitro or diazo group is inserted in the proteid mole- 

 cule. Immunization with such transformed proteid compounds, e.g., 

 xanthoprotein, can produce a precipitating serum which will react with 

 every xanthoprotein even in homologous animals. These authors 

 conclude that species specificity is probably dependent upon a certain 

 aromatic group of the proteid molecule. 



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