336 PRECIPITINS 



the end of half an hour at room temperature. If in tubes 1, 2, 4, and 

 possibly 3 a misty cloudiness should appear within five minutes, the 

 extract is very probably one of horse flesh. If a definite precipitate 

 forms within thirty minutes, the other tubes remaining clear, horse 

 flesh or the flesh of some other single-toed animal is present. 



If the preliminary titration does not show a precipitate with the 

 immune serum until at the end of one or two hours, this interval may be 

 utilized for conducting the test. 



In a similar manner tests may be made for the meat of dogs, cats, 

 or any other animals if the respective immune serums are used with the 

 extract. 



BACTERIAL PRECIPITINS 



As has previously been stated, these precipitins have slight diagnostic 

 significance, as the information they yield in the diagnosis of an infec- 

 tion or in the differentiation of bacterial species may be gained much 

 more easily with the agglutinin test. 



Bacterial precipitinogens are prepared by filtering ten to twenty-one 

 day bouillon cultures through Berkefeld filters. The filtrates must be 

 absolutely clear and sterile, for the reaction frequently requires a num- 

 ber of hours, and if bacteria are present, they may grow quickly, produce 

 turbidity, and mask a reaction. 



Immune Serum. This is prepared according to the technic described 

 under Active Immunization. Rabbits are given intravenous injections 

 of increasing doses of cultures of the bacteria themselves or of filtrates, 

 the inoculum being heated at 60 C. for an hour previous to making the 

 injection. After the third dose the serum is titrated and the injections 

 continued unless the serum is satisfactory. 



Technic. A known quantity of precipitinogen and varying amounts 

 of immune serum are employed. If too much precipitinogen is fur- 

 nished, the precipitate will not form, and one that has already formed 

 may dissolve on the addition of more precipitinogen. 



If, for example, one desires to determine if typhoid precipitin is 

 present in a given serum, the test is conducted as follows: 



Tube 1: 2 c.c. of typhoid bouillon filtrate +0.05 c.c. of unknown 



serum +0.9 c.c. of normal salt solution 

 Tube 2: 2 c.c. of typhoid bouillon filtrate +0.1 c.c. of unknown 



serum+0.9 c.c. of normal salt solution. 



Tube 3: 2 c.c. of typhoid bouillon filtrate+0.5 c.c. of unknown 

 serum+0.5 c.c. of normal salt solution. 



