TECHNIC OF PRECIPITIN REACTIONS 333 



Partial reactions between closely related species due to group pre- 

 cipitins seldom occur, and are easily detected when the technic described 

 is employed. The precipitin test, as determined by the extensive ex- 

 perience of Nuttall, is highly .specific, and it is only between very closely 

 related animals, such as the hare and the rabbit, the horse and the 

 mule, the sheep and the goat, etc., that any doubt can arise. 



When only very limited amounts of the unknown stain are available, 

 the test, according to Hauser, can be carried out in slender, clean, and 

 sterile capillary tubes. The piece of stained clothing is torn into shreds, 

 extracted, and filtered until clear. The tests are performed by drawing 

 a small amount of the unknown solution into a capillary tube, and under- 

 lying this with a small amount of immune serum. As many controls 

 as possible are put up in the same manner. A distinct whitish ring will 

 form in the positive tubes at the line of contact between the two fluids; 

 this is best seen by holding the tube against a black background. 



DETECTION OF MEAT ADULTERATION 



The principle of this method is the same as that in the foregoing test. 

 An extract of a meat will yield a precipitate when mixed with its anti- 

 serum, prepared by immunizing rabbits with an extract of the flesh or 

 with the blood-serum of some other animal. 



The method is especially serviceable in food inspection for the de- 

 tection of horse, dog, or other foreign flesh in meat mixtures, such as 

 sausage and the like. Even salted and cooked meats may be used in the 

 test, although the latter may require the use of antiserums prepared by 

 immunizing with heated or cooked antigen. 



Preparation of the Meat Extract. To prepare this, about 50 grams 

 of flesh are removed from the deeper parts of the specimen by means of a 

 sterile knife, and through a fresh opening, as this portion has been least 

 exposed to the methods of preservation, especially at the high tempera- 

 tures to which the meat may have been exposed. It should contain as 

 little fat as possible. It is then placed on a clean sterile tile and cut into 

 smaller pieces, and finally minced by passing it through a perfectly dean 

 meat-grinder or chopping it with a sterile chopping knife. After being 

 finely minced the meat is placed in a sterile Erlenmeyer flask, and cov- 

 ered with 100 c.c. of sterile normal salt solution. The mixture of meat 

 and salt solution is kept for about six hours at room temperature, or 

 overnight in the refrigerator, the flask being gently shaken from time to 

 time. 



Salted meat should be ground and freshened by placing it in a large 



