324 



PRECIPITINS 



after the tubes have stood over night. "In all the tubes at first crystals 

 form, but in the tubes containing normal serum they often disappear 

 in six to twenty-four hours, while they remain in the tubes with syphilitic 

 serum." Strickler has used this test in my laboratory, and my obser- 

 vations of his results leads me to the conclusion that it is frequently 

 difficult to interpret the reactions, and that the test has not by any means 

 the practical value of the Wassermann reaction. 



[ I W 



FIG. 88. THE NOGTTCHI BUTYRIC-ACID TEST FOR GLOBULINS. 

 The tube on the extreme left shows the formation of flocculi within a few minutes 

 after adding NaOH; the middle tube shows a strongly positive reaction after stand- 

 ing several hours (supernatant fluid quite clear) ; the tube on the extreme right shows 

 a very slight opalescence, but no flocculi (within the limits of normal). 



PROTEIN PREOPITINS 



The protein precipitins have a larger range of value and represent 

 one of the most important practical aids in forensic medicine. As men- 

 tioned elsewhere, a precipitating immune serum reacts only, or at least 

 best, with its homologous serum. The precipitin reaction is, therefore, 

 highly specific, and offers a method whereby proteins can be easily and 

 definitely determined a problem that could not be solved by chemistry. 



By means of lactoserums various milks and cheeses may be recognized 

 and their source determined. 



By using appropriate immune serums seminal fluids and stains may 

 be detected, and in medicolegal cases, where the question is one of rape, 

 this reaction possesses considerable value in differentiating seminal from 

 leukorrheal stains. 



