COMPOSITION OF MILK 21 
stance named fibrin. This seems to be similar to the nuclein 
mentioned by Fleischmann, if not the same. But as these 
substances are present to a very small extent, citric acid, urea, 
and fibrin being present to the extent of .12, .007, and .0002% 
respectively (Fleischmann and Babcock), they are of little 
importance. 
