PRECIPITATION TEST 1 73 



clear, and especially if the meat to be examined was fat or salt, 

 it is filtered through a sterile Berkefeld or through a layer of 

 infusorial earth stratified in a Biichner funnel. 



The filtrate is suitable for the test when a foam is developed 

 by shaking and when it contains about i part of protein in 300 

 parts of salt solution. To determine this, 2 cc. of the clear filtrate 

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

 acid (sp. gr. 1.153) i^ added; if a marked cloudiness and a 

 flocculent precipitate forms, the extract is too highly concentrated 

 and must be diluted with normal salt solution until the heat and 

 acid test causes only a diffuse, opalescent cloudiness which settles 

 to the bottom of the tube after 5 min. as a slight precipitate. 



Before proceeding with the test, the reaction of the meat ex- 

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

 acid it should be neutrahzed very carefully with o.i per cent, 

 sodium hydroxide or magnesium oxide solution. Only slightly 

 acid or alkaline solutions should be used. For the extraction of 

 the meat, spigot, tap or distilled water should not be used. Fresh 

 meat frequently produces a sufficiently strong protein solution 

 in X hr. In boiled, preserved and decomposed meat, the ex- 

 traction proceeds very slowly (24 hr.) and the solutions are 

 difficult to clarify. 



Technique of the Test. — If, for example, the object is to 

 determine whether a piece of meat is horse flesh or, if sausage, 

 contains the meat of this animal, the test is conducted as follows : 



Tube I.- — 2 cc. of unknown extract (i : 300) +0.1 cc. of anti-horse serum. 

 Tube 2. — 2 cc. of unknown extract (i :30o) -1'- o.i cc. of normal rabbit serum. 

 Tube 3. — 2 cc. of horse flesh extract (i : 300) + 0.1 cc. of anti-horse serum. 

 Tube 4. — 2 cc. of pork extract (i 1300) H- 0.1 cc. of anti-horse serum. 

 Tube S- — 2 cc. of beef extract (i : 300) -|- 0.1 cc. of anti-horse serum. 

 Tube 6. — 2 cc. of saline solution -|- 0.1 cc. of anti-horse serum. 



The immune serum is added to each tube very carefully and 

 run down the sides of the tube, or stratified. The tubes must 

 not be shaken. The tubes are kept at room temperature. The 



