What is The composition of blood?

Blood is a tissue in suspension: about $5\,\mathrm{L}$ in an adult, $7\,\%$ of body mass. Spun down, it separates into plasma ($55\,\%$: water, $70\,\mathrm{g}/\mathrm{L}$ of proteins — albumin, globulins, fibrinogen — and the salts, sugars, lipids, gases and hormones it carries) and cells ($45\,\%$, the haematocrit): red cells ($5\times 10^{12}$ per litre, biconcave discs of $7\,\text{µ}\mathrm{m}$ without a nucleus, each packed with $280$ million molecules of haemoglobin, living 120 days and made in the marrow at two million a second), white cells ($7\times 10^{9}$ per litre: neutrophils, lymphocytes, monocytes, eosinophils, basophils, the mobile arm of immunity), and platelets ($3\times 10^{11}$ per litre, fragments of marrow cells that plug wounds and start clotting). The red cells carry oxygen — $200\,\mathrm{mL}$ per litre of blood at full saturation, seventy times what water dissolves — and the plasma carries everything else, including the $20\,\%$ of $\mathrm{CO_2}$ that is not in the cells, the heat of the muscles to the skin, and the hormones of Chapter 19 to their targets. Blood is also a solution under oncotic pressure: its proteins, which cannot leave the capillaries, hold about $25\,\mathrm{mmHg}$ of osmotic pull, and that pull is what keeps the plasma in the vessels.