The proteids of the serum are serum globulin, serum albumin, and a ferment produced as the result of coagulation. As fibrinogen is used up in the process of coagulation, it is not found in the serum, but there is in the serum a proteid known as fibrino-globulin. This is produced from fibrinogen during the process of fibrin formation. The following tabulation gives a clear idea of the difference between the proteids of plasma and of those of serum: Proteids of Plasma Fibrinogen Serum globulin Serum albumin Proteids of Serum Serum globulin Serum albumin Fibrin ferment (nucleoproteid) Fibrino-globulin Fibrinogen is the precursor of fibrin. The fibrin of the blood clot of the bird is soft and very lacerable. The serum is usually yellow. THE FATE OF THE ERYTHROCYTE OF THE FOWL The power of vascular endothelium to ingest red blood corpuscles has been studied by Keys. When bacteria or other minute foreign bodies are injected into the blood stream of pigeons, they are rapidly withdrawn from the circulation into the tissues of the liver and of the spleen. The foreign bodies are noted to be contained within cells of a distinct type, which is found in both liver and spleen. This type of cell contains, in addition to the foreign substances injected, much yellow pigment, and when tested for iron by Pearl’s method gives a positive Prussian-blue reaction. In such specimens there is a display of contrast to other tissues. There is an extensive content of cells possessing the distinct tone of Prussian-blue iron reaction. These cells are distributed rather evenly throughout both the spleen and the liver, but more numerously in the liver.