n6 



PRECIPITINS. 



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 albumin body. In order therefore to make a medico- 

 legal diagnosis of " human blood stains," chemical evidences 

 " Origin" and must * n addition be brought forward, that the stain really 

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

 tional" Spec- that besides animal specificity ("origin specificity"), pre- 



ificity. cipitation also demonstrates the "constitutional specificity" of 

 proteids. 



If instead of employing pure animal, or plant proteids for the immu- 

 nization of animals, variously changed albumins are used (heated albumins, 

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

 ing antibodies of a characteristic nature, different from those developed 

 after inoculation with the pure albumin. For example; the serum of a 

 rabbit immunized 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 native 

 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 fabrica- 

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



