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PRECIPITINS 



SIGNIFICANCE AND APPLICATION OF PRECIPITINS— 

 TECHNIC OF REACTION— SPECIFIC IDENTIFICATION OF 

 BLOOD AND OTHER PROTEINS 



When a protein is brought in relation, in vitro, 

 with blood-serum of an animal which has been immu- 

 nized against that particular protein, the protein is 

 thrown out of solution, the fluid becomes cloudy, and a 

 sediment finally settles to the bottom of the tube. This 

 is known as the precipitation phenomenon, and is due 

 to the presence in the blood-serum of substances known 

 as precipitins. Precipitins are antibodies formed in 

 the blood in response to injection of unorganized pro- 

 tein material. They are antibodies of the second order 

 of Ehrlich, and are analogous to agglutinins, which 

 act upon organized proteins or bacteria. 



The precipitation phenomenon is made use of in the 

 identification of various proteins. Each species of ani- 

 mal has a specific protein, which can be detected by the 

 precipitation reaction. Practically, the test has been 

 made use of chiefly in ( I ) detection of adulteration of 

 meat products such as sausages, etc. ; and ( II ) in the 

 medicolegal identification of blood. 



(I) Detection of Adulteration of Meat Products 



This test can be applied to determine whether 

 sausages represented as being made purely of beef or 



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