TECHNIC OF PRECIPITIN REACTIONS 335 



As has repeatedly been mentioned, it is advisable to immunize a 

 number of rabbits at the same time, for only a small number will yield a 

 satisfactory serum after the third injection. 



Immunization may be performed with extracts of flesh that have been 

 filtered and heated at 56 C. for an hour to secure partial sterilization. 

 Such injections, when given subcutaneously, are likely to produce ex- 

 tensive sloughing, and with any method of immunization the mortality 

 is high. 



After the third inoculation it is well to remove a small amount of 

 blood from the ear and make a preliminary titration. This is performed 

 in exactly the same manner as in making the forensic blood test pre- 

 viously described. An antiserum is satisfactory if 0.1 c.c. produces a 

 well-marked cloudiness and a precipitate in ten minutes with 2 c.c. of a 

 1 : 1000 dilution of the serum or extract of flesh. 



In addition to being highly potent, the immune serum must be crystal 

 clear and sterile. To avoid opalescence the animal should be bled only 

 after a period of fasting. 



Technic. If, for example, the object is to determine whether a 

 piece of meat is horse flesh or, if sausage, contains the meat of this ani- 

 mal the test is conducted as follows : 



Tube 1: 2 c.c. of unknown extract, 1:500+0.1 c.c. of antihorse 



serum. 

 Tube 2: 2 c.c. of unknown extract, 1 : 1000+0.1 c.c of antihorse 



serum. 

 Tube 3: 2 c.c. of unknown extract, 1 : 5000 +0.1 c.c. of antihorse 



serum. 

 Tube 4: 2 c.c. of horse flesh extract, 1 : 1000+0.1 c.c. of antihorse 



serum (positive control). 

 Tube 5: 2 c.c. of unknown extract, 1:500+0.1 c.c. of normal 



rabbit serum. 



Tube 6: 2 c.c. of pork extract, 1 : 500+0.1 c.c. of antihorse serum. 

 Tube 7: 2 c.c. of beef extract, 1 : 500+0.1 c.c. of antihorse serum. 

 Tube 8: 2 c.c. of unknown extract. 



Tube 9: 2 c.c. of sterile salt solution+0.1 c.c. of antihorse serum. 

 The immune serum is added to each tube very carefully and run 

 down the sides of the tube, rather than dropped into them. The tubes 

 should not be shaken. 



If the preliminary titration of the immune serum fulfils the ideal 

 requirement of yielding a well-marked cloudiness within five to ten 

 minutes with a 1 : 1000 extract, the foregoing test should be recorded at 



