BACTERIAL PRECIPITIN REACTIONS. 109 



Bacterial Precipitin Reactions. 



For the production of precipitating sera, animals are immu- 



Productionof mze d either with the bacterial bodies themselves, or fluids 



Precipitin containing the bacterial proteid (precipitinogen) , such as 



Sera. the nitrates of bouillon cultures and the various forms of 



bacterial extracts. The serum from individuals undergoing 



an infection or convalescing from one, contains precipitins against the 



respective infective agent. 



Inasmuch as the reaction consists of the formation of a precipitate, it is 

 important that both of the ingredients (precipitin and precipitinogen) be abso- 

 lutely dear 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 is withdrawn and immediately centrifugalized in order to ascertain whether 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 col- 

 lected. Erythrocytes and bacteria produce, at some times, turbid serum. 

 Simple sedimentation or centrifugalization suffices to overcome this. 



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

 had in filtration through paper or bacterial niters, 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 reaction requires 

 ogens. a long period of time. If bacteria are present they may grow 

 quickly, and produce turbidity. The precipitinogen loses 

 after a time its property of combining with precipitins and forming preci- 

 pitates. In such a case the precipitinogen can be employed for immunization 

 purposes. 



A constant amount of precipitinogen is placed into each of 

 Technique of a row of test tubes, and to these are added diminishing amounts 

 the Reaction, of the serum. 



A set quantity of serum and varying amounts of precipitinogen 

 can also be employed. The result of the reaction depends to a very large 

 extent upon the quantitative relationship of these ingredients. If relatively 

 too much precipitinogen exists, a precipitate will not form. An already formed 

 precipitate will dissolve on the addition of more precipitinogen. 



