=Structure of the Red Blood Cell.=—The red blood cell is composed of a spongy stroma holding in its meshes the red coloring matter. The stroma, or framework, of the erythrocyte consists principally of nucleo-albumin; it contains lecithin, cholesterin, and salts. The red matter consists of an albuminous crystalline substance called hemoglobin, which forms about 90 per cent. of the total solid matter of the dried corpuscle. Each red cell offers a certain absorbing surface for oxygen. As the blood circulates through the delicate walls of the lungs and the air-sacs, it takes up oxygen; the blood at the same time delivers to the air carbon dioxid which has been brought from the tissues where active cell metabolism has been going on. This oxygen taken up by the erythrocyte forms a loose chemical union and is known as oxy-hemoglobin. In this form it is carried to the tissues of the body where it is given up by the erythrocyte to the tissues where oxidation is going on. _Hemoglobin_ is a crystallizable proteid substance containing carbon, hydrogen, oxygen, nitrogen, sulphur, and iron. =Formation of the Cells of the Blood.=—The red blood cells are formed in the red marrow of the bone. Polymorphonuclear leucocytes are formed in the red marrow of the bones, and the lymphocytes in the lymph glands and lymph follicles. The bird carries a normal body temperature of 105° to 107° F. The average temperature of 50 mature hens and cocks was 106.8° F. The blood is of a deep red color. =Composition of the Blood.=—The average composition of the blood of the domestic fowl as given by Owen, is as follows: Whole shed blood: Water 780 parts Clot 157 parts Albumin and salts 63 parts ————— 1000 parts Moist blood cells: Average total weight 456.69 Water 342.52 Solid matter 97.50 Plasma: Total weight 543.30 parts Water 495.72 parts Solid matter 30.72 parts Blood when drawn and allowed to stand soon coagulates. In the blood of birds this process is very rapid, the blood coagulating, in most instances, in about one-half minute. Blood coagulates only in the presence of calcium salts. During life, the liquor sanguinis is termed plasma; but after it has been shed from the body and coagulation has taken place, the liquid residue is called serum. Serum is plasma with its modifications as the result of coagulation, and as this latter process is brought about by the production of fibrin, we may say that serum is plasma minus fibrin-forming elements.