146 IMMUNE SERA 



centrated dilutions are used, the deposit may form 

 an irregular mass at the bottom of the tube. 



The reaction may be followed microscopically by 

 means of the hanging-drop method. By this method 

 a reaction can be observed within ten to fifteen 

 minutes, which macroscopically becomes visible 

 only after two hours. 



Delicacy of ike Precipitin Test. Whereas the 

 ordinary chemical tests for blood cease to give reac- 

 tions in dilutions of about i : 1000, powerful antisera 

 greatly exceed this limit, as the reported results of 

 independent observers have shown. Working with 

 an antihuman serum, Strube reports a reaction 

 with a blood diluted 20,000 times, and Stern one 

 with a blood diluted 50,000 times. Ascoli obtained 

 a reaction with a specific serum with egg albumin 

 diluted 1,000,000 times. 



Other Applications of the Precipitin Test. It can 

 be readily understood that this test finds ready 

 application in the detection of horse, dog, or cat 

 meat in sausage. 



The principle and the method are the same in all 

 these various applications. We treat animals with 

 the albumins which we wish to differentiate, and so 

 obtain sera specific, each for its particular kind oi 

 albumin. These sera, then, produce precipitates 

 only in solutions of their respective albumins. For 

 example, if we wish to determine whether a given 

 sample of meat is horse-flesh or not we must inject 



