16 Proteins of Cow’s Milk 
about 30 per cent of iron, is soluble in an excess of alkali, and 
behaves like a compound of protein with iron. 
Siegfried’ later obtained a product from cow’s milk which he 
considered to be identical with fucleon from muscle extract, 
except that it yielded fermentation lactic acid instead of para- 
lactic acid, when hydrolyzed with baryta. He obtained this by 
precipitating casein with acid and the coagulable proteins by boil- 
ing. After removing phosphates by adding calcium chloride and 
ammonia, and neutralizing the filtered solution, carniferrin, the 
iron compound of nucleon, was precipitated by adding ferric 
chloride and boiling. 
We have confirmed Siegfried’s observation by applying the 
above procedure to milk serum from which the proteins and 
phosphates had been removed as he directs and much of the lac- 
tose by concentration and crystallization. This solution, how- 
ever, contained a not inconsiderable quantity of proteose-like 
protein which could be separated by saturation with ammonium 
sulfate and readily obtained almost free from phosphorus by 
treating its solution with baryta, removing the latter with sulfuric 
acid, and precipitating with an excess of alcohol, a procedure 
substantially like that employed by Siegfried. Practically all of 
this proteose was included in the precipitate produced by adding 
ferric chloride and boiling. However, although a considerable 
amount of ferric chloride could be added to the filtrate from the 
precipitate produced by saturating with ammonium sulfate 
before a reaction with ferrocyanide occurred, no nucleon-like 
precipitate could be obtained in this solution freed from proteose. 
Although Siegfried makes no statement as to the presence or 
absence of proteose-like substances in solution after removing 
coagulable proteins it would appear that he did not realize that 
such were present. Since he took no step to remove these, our 
exverience leaves little doubt that such protein formed a part 
of his carniferrin. It is to be noted that the aqueous extract of 
ox muscle when freed from coagulable proteins by boiling con- 
tains a small amount of protein which can be precipitated by 
saturating with ammonium sulfate. 
Our work with milk has convinced us that a part of the phos- 
8 Siegfried, Z. physiol. Chem., 1895-96, xxi, 360. 
