THE PHENOMENON OF PRECIPITATION 251 



Of importance in connection with the problem of the nature of 

 precipitinogen, also, is the claim of Myers/ 4 that specific precipitins 

 may be produced in rabbits by treatment with Witte peptone, a sub- 

 stance complex in constitution, but consisting largely of albumoses. 

 This observation has failed of confirmation in the hands of Ober- 

 meyer and Pick, Michaelis, 15 Norris, 16 and others, and cannot, there- 

 fore, be accepted as an established fact. 



Whichever method of precipitinogen production is used bacterial 

 precipitins appear in the serum of the immunized animal only after 

 careful and continued immunization, usually later than the demon- 

 strable appearance of the bactericidal or agglutinating properties of 

 the serum. The most convenient material for such immunization^ 

 consists of salt solution emulsions of agar cultures, killed at 60 to 

 70 C. These may be injected subcutaneously, intraperitoneally, or 

 intravenously, the last method leading to the most satisfactory and 

 rapid results and, therefore, best employed unless great inherent 

 toxicity of the particular bacteria contraindicates. When rabbits 

 are used it is generally necessary to inject 3, 4, or 5 times at 5 or 6- 

 day intervals, and to bleed the animals on the 8th or 9th day after 

 the last injection. 



The bacterial precipitins so produced are, as we have said above, 

 specific but, again, specificity, as in the case of agglutinins, is 

 limited by the so-called "group reactions." In the chapter dealing 

 with agglutination we have seen that the serum of a typhoid-immune 

 animal which agglutinates typhoid bacilli strongly will also aggluti- 

 nate, though far less powerfully, paratyphoid bacilli and, in some 

 cases, even colon bacilli, this appearance of "minor" agglutinins 

 being probably due to a close group relationship of these bacteria to 

 the typhoid bacillus. In the case of bacterial precipitins the same 

 thing is true, and has been made the subject of special studies by 

 Zupnik, 17 Kraus, 18 Norris, 19 and others. As in the case of ag- 

 glutination, however, this fact does not in any way interfere with 

 the practical value of the specificity of the reaction because elimina- 

 tion of the secondary group reactions, which in agglutination is 

 obtained by dilution of the antiserum, can here be obtained, as Kraus 

 points out, by diminishing the quantity of the undiluted precipitat- 

 ing serum added to the bacterial filtrates. Thus, while one volume 

 of serum added to one, two, or three volumes of culture filtrate may 

 still give error due to non-specific group reactions, a proportion of 



"Myers. Centralbl f. Bakt., Vol. 28, 1900. 



15 Michaelis. Deutsche med. Woch.j 1902. 



16 Norris. Jour, of Inf. Dis., Vol. 1, 1904. 



17 Zupnik. Zeitschr. f. Hyg., 49, 1905. 



18 Kraus. Wien. klin. Woch., 1901, No. 29. 



19 Norris. Jour, of Inf. Dis., Vol. 1, 1904. 



