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LABORATORY COURSE IN SERUM STUDY 



LESSON XIV 

 TITRATION OF PRECIPITATING SERA FROM RABBITS 



SPECIFICITY OF PRECIPITINS 



PRECIPITATING sera are active against proteins in high dilu- 

 tions. Their specificity is great but is limited by group reactions 

 so that a precipitating serum for the protein of any species of 

 animal or bacteria will give precipitation, with closely related 

 species in low but not in high dilutions. On this is based Nuttall's 

 well-known study of blood relationships. 



Students working in groups bleed serum-treated rabbits (Lesson I) 

 from the carotid 10 days after the last injection, taking about 20 c.c. 

 of blood in small centrifuge tubes. The animal should be in a fasting 

 state in order that the serum will be clear. Allow the blood to clot and 

 centrifugalize. 



Experiment 1 



One half of the students in the class make dilutions in large test 

 tubes of sheep serum or human serum respectively (according to par- 

 ticular serum with which rabbit has been treated) as follows: 1-10, 1-20, 

 1-50, 1-100, 1-200, 1-500, 1-1000. In order to test the specificity of the 

 reaction the other half of the students make similar dilutions of serum from 

 other species of animal guinea pig, dog, cat, sheep, horse, as available. 



Then set up the following mixtures in small "precipitation" tubes 

 (tubes of about 5-8 mm. diameter) : 



In making these mixtures, put the anti-serum into the tubes first 

 and then run the dilution into the tubes with a nipple pipette in such a 

 way that the latter is layered over the former as in a Heller's test for 

 albumin in urine. This is the so-called "ring test." . The precipitum 

 shows as a white line at the contact of the two fluids. After this ring 



