PRECIPITIN REACTION 121 



Bacterial Precipitin Reactions. 



For the production of precipitating sera, animals, preferably 

 Production of rabbits, are injected either with broth cultures or salt solution 

 Bacterial emulsions of agar cultures of the bacteria. Five to six in- 

 Precipitat- jections of gradually increasing quantities are given intra- 

 ing Antisera. peritoneally or intravenously, at intervals of from five to six 

 days. The dose varies with the virulence of the bacteria. 

 The intravenous method frequently giyes the stronger serum but the mode 

 of administration depends also on the pathogenic properties of the micro- 

 organism in question. The immunized animals should be bled about 

 seven to twelve days after the last injection of bacteria. The filtrates of 

 bouillon cultures and the various forms of bacterial extracts will also, when 

 injected, produce precipitins. The serum from individuals undergoing 

 an infection, or convalescing from one, contains precipitating bodies against 

 the respective infective agent. 



Inasmuch as the precipitin reaction consists in the formation of a pre- 

 cipitate, it is important that both of the ingredients (precipitin and precipi- 

 tinogen) be absolutely clear and have no tendency to spontaneously become 

 turbid, or form a precipitate. 



In order to get a clear serum one should avoid withdrawing 

 Obtaining the blood during the period of digestion of the animal, because 

 Clear Sera, it is chylous at such a time. In man the best occasion for 



obtaining the blood is in the morning before breakfast. As 

 for animals, it is advisable to give them no solid food (or milk) for twenty- 

 four hours previous to venesection. Then a very minute quantity of blood 

 is withdrawn and immediately centrifugalized in order to ascertain whether 

 the serum is clear or not. If it is satisfactory, larger amounts may be 

 collected. The presence of erythrocytes and bacteria causes a serum to be 

 turbid. Simple sedimentation or centrifugalization suffices to overcome 

 this. 



If in spite of these precautions turbidity still persists, recourse may be 

 had to filtration through paper or bacterial filters, preferably new ones. 

 This method should, however, be used as a last resort, because filtration 

 always tends to diminish the strength of a serum. 



Bacterial precipitinogens are prepared by filtration either of 



Bacterial bouillon cultures or bacterial extracts. The filtrates must be 



Precipitin- absolutely clear; also sterile, as frequently the precipitin 



ogens. reaction requires a long period of time. If bacteria are present 



they may grow quickly, and produce turbidity. After a 

 time the precipitinogen loses its property of combining with precipitins 

 and forming precipitates. In such a case the precipitinogen can still be 

 employed for immunization purposes. 



