THE TECHNIQUE OF SERUM REACTIONS 253 



gesled the use of throttle pipettes of comparatively large diameter into 

 each of which at least three or four different dilutions can be sucked 

 with a nipple, a small air bubble being left between the mixtures. By 

 sealing the distal end of these pipettes in a flame the various dilutions 

 are kept at a distance from each other, and the pipettes may be set on 

 end in a tumbler and observed just as are the test tubes (Fig. 68, p. 285). 

 The special methods of carrying out agglutination tests with pneumo- 

 cocci have been described on p. 363. 



Precipitin Tests. In an earlier section on precipitins we have seen 

 that precipitates are formed when clear filtrates of bacterial extracts 

 or of both cultures are mixed with their specific immune sera. Such 

 precipitin reactions are not limited to the realm of bacteria, but have a 

 broad biological significance, in that specific precipitating sera may be 

 produced with proteids of varied source. 



For carrying out a precipitin test, the following reagents are required : 



1. A specific precipitating antiserum (antibacterial or antiproteid) ; 



2. A bacterial filtrate or proteid solution. 



PRODUCTION OF PRECIPITATING ANTisERA. 1 Antibacterial precip- 

 itins may be produced in animals by a variety of methods. Animals, 

 preferably rabbits, are injected with cultures of the bacteria in 

 gradually increasing quantities. Five or six injections are given at 

 intervals of from five to six days, the dosage and mode of administra- 

 tion being adapted in each case to the pathogenicity of the micro- 

 organisms in question. Myers 2 claims that specific precipitin for pepton 

 in the culture media may be formed which may lead to error. This 

 could not be confirmed by Norris. 3 The immunized animals should 

 be bled about 7 to 12 days after the last injection. 



Precipitating antisera against protein solutions are prepared by 

 similar methods. The sera or protein solutions used should be sterile. 

 This may be accomplished by filtration through small porcelain filters. 

 Injections into animals may be made subcutaneously, intraperitoneally, 

 or intravenously. The subcutaneous route has no advantages unless 

 the substances to be used are contaminated. 



Nuttall advises the use of rabbits. The animals are weighed from 

 time to time, and if considerable loss of weight ensues, the intervals 

 should be increased. Doses from 2 to 5 c.c. should be given. In 

 giving the later injections the danger of anaphylaxis must be remem- 



1 R. Kraus, Wien. klin. Woch., 1897; Norris, Jour. Inf. Dis., 1 and 3, 1904. 

 2 Myers, Lancet, ii, 1900. 3 Norris, loc. cit. 



