TECHNIC OF PRECIPITIN REACTIONS 311 



sterile Erlenmeyer flask and covering it with sterile distilled water, re- 

 newed several times in the course of fifteen minutes without shaking the 



Since the presence of a great deal of fat interferes with the reaction, 

 it is advisable to remove it beforehand by extracting it with ether and 

 chloroform for from twelve to twenty-four hours (Miessner and Herbst). 

 Pork sausages are usually quite fatty, and may require this preliminary 

 treatment. To make the extraction, take about 75 to 100 grams of the 

 minced meat or sausage and place it in a large Erlenmeyer flask and cover 

 with equal parts of ether and chloroform. After twenty hours the ether 

 and chloroform are poured off, the meat is washed once or twice with 

 sterile normal salt solution, and then extracted in 100 c.c. of salt solu- 

 tion, as described elsewhere. 



To determine whether a sufficient quantity of protein substances has 

 passed into solution place 2 c.c. in a test-tube and shake vigorously. If 

 a foam develops and persists for some time, the extraction may be said 

 to be complete. It must then be filtered until it becomes perfectly clear. 

 With extracts of fresh lean meat this is usually accomplished by filtering 

 through a hard filter-paper moistened with salt solution. If it is not 

 crystal clear, and especially if the meat to be examined is fat or salt, it 

 may be necessary to filter through a sterile Berkefeld filter. 



To make the test the extract should contain about one part of pro- 

 tein in 500 parts of salt solution. To determine this, 2 c.c. of the clear 

 filtrate are placed in a test-tube and heated, a drop of dilute nitric acid 

 being added. If a marked cloudiness and a flocculent precipitate de- 

 velops, the extract is too concentrated and must be diluted with clear 

 normal salt solution until the heat and acid test causes only a diffuse, 

 opalescent cloudiness that settles at the bottom of the tube after five 

 minutes as a slight precipitate. 



Before proceeding with the experiment the reaction of the solution 

 should be tested with litmus paper, and if it is found to be acid, it should 

 be neutralized very carefully with ^ sodium hydroxid. 



Extracts of the meats that are known or likely to be present, such as 

 extracts of pork and beef, should be prepared as controls. 



Preparation of Immune Serum. An immune serum against that 

 variety of flesh that is to be determined in the unknown specimen is 

 prepared by injecting rabbits intravenously with the serum of an ani- 

 mal of that species. For example, if the object is to test for dog meat, 

 an anti-dog serum is prepared by immunizing rabbits with sterile dog 

 serum. 



