PRECIPITATION TEST 173 



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

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

 nfusorial earth stratified in a Biichner funnel. 



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

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

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

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

 icid (sp. gr. 1.153) i s added; if a marked cloudiness and a 

 locculent precipitate forms, the extract is too highly concentrated 

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

 icid test causes only a diffuse, opalescent cloudiness which settles 

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



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

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

 icid it should be neutralized very carefully with o.i per cent, 

 jodium hydroxide or magnesium oxide solution. Only slightly 

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

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

 neat frequently produces a sufficiently strong protein solution 

 n i hr. In boiled, preserved and decomposed meat, the ex- 

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

 difficult to clarify. 



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

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

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



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

 Tube 2. 2 cc. of unknown extract (i : 300) -\- o.i cc. of normal rabbit serum. 

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

 Tube 4. 2 cc. of pork extract (i 1300) + o.i cc. of anti-horse serum. 

 Tube 5. 2 cc. of beef extract (i : 300) + o.i cc. of anti-horse serum. 

 Tube 6. 2 cc. of saline solution + o.i 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 



