Publisher Summary In 1894, Schmiedeberg prepared an iron-containing protein from pig's liver, containing about 7% iron. This poorly defined compound was obtained in a denatured condition. The first decisive step was made with Laufberger's discovery of a readily crystallizable protein, containing as much as about 20% of iron, in the ferric state. It was obtained from horse spleen and other organs of different animals by means of a simple method that essentially depends on the fact that this iron protein readily crystallizes from its solution on addition of cadmium sulfate. In deference to Schmiedeberg's “ferratin,” but in distinction from that questionable compound, Laufberger called the well defined, reproducible compound “ferritin.” The protein, apoferritin, appears to be synthesized when it is to be used for the storage of iron. When a new kind of protein is discovered, there is always the suspicion that it may be an enzyme or coenzyme. So far no chemical process, either of specific hydrolytic or oxidative-reductive character, is found for which apoferritin would function either as an enzyme or as a coenzyme. Its sole function appears to be storage of iron. Why this particular protein, apoferritin, is able to store iron is not understood.