THE PRECIPITIN REACTION. 79 



Recently the effect of variations in the H-ion concentration 

 of the salt solution on the reaction has been studied. Using the 

 flocculation test Mason (1922) found no significant effect within 

 a range of P H 4.5 to 9.5. However the flocculation test is not 

 sensitive enough to show a slight effect had there been one. 

 Evans (1922) and Mason and Sanford (1924) find that the H-ion 

 does have an effect on various serological reactions and recom- 

 mend buffered physiologic salt solutions for use in serological 

 work. 



With regard to the mode of injection of animals it has generally 

 been found that intravenous injections give higher titers than 

 any others. Such injections are given in increasing doses as 

 four, six, eight cubic centimeters of serum on successive days 

 or at two to five day intervals. The titer reaches its climax 

 about the tenth day after the last injection. Rabbits and 

 chickens have been found to be the most practical precipitin 

 producers. 



MATERIAL AND METHODS USED IN THIS INVESTIGATION. 



Rabbits and chickens have been used to produce the antisera. 

 They have been injected with sterile blood sera of healthy sheep, 

 goat, pig, horse and dog. The injections were usually intra- 

 venous though many were intraperitoneal. They were given for 

 the most part at three day intervals the dosage being 4 cc., 6 cc., 

 and 8 cc. of the particular blood serum used as antigen. Ten 

 days after the third injection the rabbits were bled from the 

 median ear artery and the fowls from the wing vein, a five cc. 

 sample being withdrawn for a preliminary titration. In many 

 cases the antisera so obtained possessed a titer of 6,400 or over. 

 That is, a definite ring appeared in a dilution of one part of 

 antigen in 6,400 parts of salt solution, at I hour, but did not 

 appear in any greater dilutions. In other cases one or two more 

 injections were given, the first one being 2-4 cc. and given intra- 

 peritoneally, the second 5-10 cc. and given intravenously. No 

 symptoms of anaphylaxis have ever been noted. Usually the 

 titer of these reinjected animals had now increased to 6,400 or 

 over. All such titers were thought to be satisfactory and the 

 animals possessing them were bled completely as soon as possible 



