An examination of Bardach's new protein test

Abstract

In a recent paper, Bardach 1 drew attention to the fact that the formation of typical iodoform crystals from iodopotassium iodide and acetone in an alkaline solution may be prevented by albumin. In the presence of a sufficient proportion of albumin in such solutions, the production of characteristic hexagonal platelets or stellar masses of iodoform does not occur, but, instead, fine yellow needles, apparently of some other substance, gradually appear. Bardach found that the power of bringing about this interesting crystalline reaction is also exhibited in a general way by acidalbumin, protoal-bumoses, peptones, phytovitellin, casein, yeast nuclein, hemoglobin, tendomucoid, gelatin, and by the following protein-containing materials: pancreatin, sperm, blood, sputum, normal urine and albuminous urine. He did not name any proteins that fail to give the reaction.

The best conditions and procedure for the test are stated by Bardach to be as follows: To 5 c.c. of the moderately concentrated albuminous liquid, 2 add at first 2 or 3 drops of a dilute aqueous acetone solution (0.5 per cent), then sufficient Lugol reagent 3 to supply a moderate excess of iodine, 4 and lastly considerable ammonium hydroxid (usually about 3 c.c. of concentrated solution).

If iodine is employed in moderate excess, the ammonium hydroxid usually produces at once a black precipitate of iodonitro-compounds, upon which the yellow needles are gradually deposited. If just the right amount of iodine is present, the liquid soon becomes yellowish and the black precipitate formed at once by the ammonium hydroxid gradually undergoes complete or nearly complete transformation into the yellow needles. Under both conditions the yellow needles form promptly, usually within an hour. In the presence of too large an excess of iodine the reaction may be prevented or hidden in the heavy black precipitate of iodonitrocompounds. Too little iodine or too much protein also prevents the reaction.′