FIG. 87. PRECIPITIN REACTION. PREPARATION OF EXTRACT OF BLOOD-STAIN. 



The tube on the left shows the color of an extract of a blood-stain; the middle 

 tube shows this extract so diluted as to yield a faint albumin reaction with nitric acid; 

 the tube on the right shows the foam test with the same diluted extract (about 1 :1000). 



