PROTEID PRECIPITINS. 113 



It is greatly to the credit of Wassermann and his co-workers 

 Forensic Use A. Schutze and Uhlenhuth, who recognized that this speci- 

 of Albumin ficity of precipitins was of great medico- legal value. 

 Differentia- 



tion Thus in a case where for example, a bloody shirt is found in the home 



of a man charged with murder, and the prosecution sees in that the 



proof of crime, while the defendant pleads that the stains belong to the 



blood of a sheep, the proof as to their source is of the utmost deciding evidence; and 



while chemical or microscopical examinations are here of little or no use, serum 



diagnosis wins the day. 



The blood-stained clothing is extracted in water, part of the extract is mixed with a, 

 the serum of a rabbit immunized against human serum and another part is mixed with b, 

 the serum of a rabbit immunized against sheep's serum. If the mixture a shows a pre- 

 cipitate, it can be definitely stated that the blood stain contained serum derived from a 

 human being; while if mixture a is clear and b shows the precipitate, it is strongly corrob- 

 orative of the presence of sheep's serum. 



This example suffices to indicate the value of this biological 

 Blood fact. In addition the reaction is made use of in the deter- 

 Relationship. mination of the nature of meats (detection of horse meat sub- 

 stitution for beef). 



Furthermore, this method has explained a number of scientifically inter- 

 esting problems. Just as group agglutination demonstrated the close 

 relationship existant between various bacteria, so also serum precipitation 

 proves a distinct relationship between the different species of animals 

 (horse and donkey, dog and fox, hare and rabbit, ape and man, etc.). 



Thus the serum of a rabbit immunized against human serum, precipitates not only 

 human serum but also that of monkeys; the serum of a chicken immunized against rabbit's 

 serum precipitates not only that, but also hare's serum. In order, however, to differentiate 

 between rabbit's and hare's serum, Uhlenhuth advises the immunization of a rabbit with 

 hare's serum. The serum of such an immunized rabbit, precipitates only hare's serum 

 and not rabbit's, for the reason that " Isoprecipitins, " i.e., precipitins against the same 

 kind of animal, are, as a general rule not developed. Similarly the differentiation 

 between human and ape's serum can be accomplished by the immunization of ape's 

 with human serum. 



Attempts to determine the origin of albumin in urine, and the foreign 

 proteids circulating in the blood of artificially fed infants have also been 

 made by means of the precipitation reaction. 



The technique remains the same, independent of the purpose it is em- 

 ployed for. It consists in the mixing of the clear precipitating serum and 

 the clear proteid, or albumin precipitinogen. 



In order to obtain accurate results, strongly precipitating sera must be had. These 

 are best made by immunizing rabbits with the precipitinogen fluid (albumin solution, 

 milk, meat juice, etc.). Three to four intravenous injections with i c.c. of the solution 

 at intervals of six days usually suffice to produce a precipitating serum of high titer. 

 The injections can also be given by the intramuscular or subcutaneous method, but here 

 larger quantities are necessary. 

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