8 Proteins of Cow’s Milk 
portion of protein which remains in solution after removing 
casein and the heat-coagulable proteins, for until we know how 
to remove this we cannot expect to deal successfully with the 
non-protein nitrogenous constituents of milk. We have there- 
fore devoted much time to a painstaking study of this problem. 
No attempt will be made to review the literature relating to 
this subject which has appeared in widely scattered journals, for 
in most cases the published details are too scanty to permit a 
critical comparison of the results with one another, or with those 
which we have obtained. References to the greater part of this 
literature can be found in the summaries of the published data 
relating to the chemistry of milk.! 
EXPERIMENTAL. 
A liters of skimmed milk, obtained in January from a mixed 
herd of a neighboring dairy, were saturated with ammonium 
sulfate and the precipitate was allowed to drain over night on 
a large folded paper. It was then ground in a Nixtamal mill 
with water, the volume brought to 3 liters, and stirred for some 
time until all was dissolved except a little fat. The solu- 
tion was then filtered through a dense felt of paper pulp and 
the latter washed with water. The filtrate was opalescent, but 
transparent. The proteins were again separated by saturating 
with ammonium sulfate, redissolved in 4 liters of water, and the 
slightly turbid fluid was treated with about 600 cc. of 1 per cent 
sulfuric acid which caused the casein to separate sharply. After 
standing on filters over night in a cold room, protected by toluene, 
the casein contracted to a dense mass and. retained relatively 
little of the solution. 
The clear filtrate was gradually treated with ammonia until 
neutral to litmus, but as no precipitate formed, the absence of . 
unprecipitated casein, of “‘acid albumin,” and also of calcium 
phosphate was demonstrated. The neutral solution was acidified 
slightly with sulfuric acid and saturated with ammonium sulfate, 
The precipitate was pressed on filter paper, dissolved in water, 
4 Raudnitz, R. W., Ergebn. Physiol., 1903, 11, 198. Rosenau, M. J., and 
others, Bull. Hyg. Lab., U. S. P.H., No. 41, 1908, No. 56, 1909. Lane- 
Claypon, J. E., Milk and Its Hygienic Relations, London, 1916. 
