PRECIPITIN REACTIONS 285 



is ordinarily only necessary to examine the material in question in 

 reference to its behavior toward an antihuman serum. If, on the 

 other hand, the antihuman investigation has shown that the material 

 was not of human origin, and it is desired to ascertain from what 

 animal species the blood was derived, corresponding sera must, of 

 course, also be available. 



PREPARATION OF THE ANTISERA. The antisera in question are 

 usually obtained from rabbits after injection with either human 

 serum, pig serum, or bovine serum, etc., as the case may be. The 

 injections are given intraperitoneally or intravenously at intervals 

 of five or six days, using 10, 8, and 5 c.c. respectively in the first 

 instance, and 5, 3, and 2 c.c. if the latter method is preferred. It is 

 always best to inject several rabbits at the same time, especially since 

 not every animal furnishes a serum with a sufficiently high titer. 

 According to Uhlenhuth this should be such that 0.1 c.c. of the anti- 

 serum shall produce a distinct turbidity either instantaneously or at 

 most after one to two minutes, when added to 1 c.c. of a 1 to 1000 

 dilution of the corresponding antigenic serum. Added to 1 c.c. of a 

 1 to 10,000 and 1 to 20,000 dilution a turbidity should be discernible 

 after three and five minutes respectively, while a control specimen, 

 containing only 0.85 per cent, saline (the diluent in question) and 0.1 

 c.c. of the antiserum must, of course, remain clear. The reaction is 

 best observed by holding the tubes (without shaking) against a dark 

 background, when it will be seen that the turbidity first appears 

 as a faint opalescence at the bottom of the tubes, but in the course 

 of five minutes extends throughout the specimen, becoming increas- 

 ingly denser and ultimately settling to the bottom as a precipitate. 



The desired titer is frequently obtained already on the sixth day 

 following the last injection. If an examination of a test specimen 

 taken from the ear does not indicate the desired strength at this 

 time, it may be necessary to give a fourth, a fifth, and even a sixth 

 injection, but it may also happen that the particular animal cannot 

 be brought to the titer that is necessary, with any number of injec- 

 tions. If, however, the examination shows that the serum can be 

 used, the animal is bled to death, the serum separated by centrifu- 

 gation, cleared by passing through a Berkefeld filter, and finally 

 stored in little glass beads or ampoules in portions of 1 c.c. each. 

 No preservative is added, and it is accordingly necessary through- 

 out to observe aseptic precautions. 



