PRACTICAL APPLICATIONS 



301 



which gradually settles to the bottom of the tube, under a clear super- 

 natant fluid (Fig. 85). 



The velocity and intensity of the reaction vary with the quantity of 

 the protein contained in a given specimen. The granular precipitate 

 appears within a few minutes in a specimen containing a considerable 

 increase in protein, whereas one hour may be required to obtain a dis- 

 tinct reaction in specimens weaker in protein. In obtaining the reaction, 

 the time period should not be greater than two hours. A faint opales- 

 cence without the formation of a distinct precipitate is to be regarded as 

 within the limits of the normal. 



FIG. 85. THE NOGUCHI 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 PRECIPITINS 



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. 



