Blood-tonics, blood-restoratives, analeptic tonics. These are generally remedies which improve the quality of the blood; but the name blood-tonics or haematinics is generally applied specially to such remedies as increase the quantity of red blood-corpuscles and haemoglobin in the blood. The quality of the blood depends upon a number of conditions: upon the amount and nature of the food ingested, on the digestion, on the formation and excretion of the various products of tissue-change, and more especially on the formation and destruction of the red blood-corpuscles themselves.

The red blood-corpuscles are probably formed in the spleen, the medulla of bones, the liver, and possibly other parts of the body, from leucocytes which lose their nucleus, take up haema-globin, and alter their form to that of the red corpuscles.

The red corpuscles are probably destroyed, at least to a great extent, in the liver, and probably also in the spleen. The colouring matter of bile contains a quantity of iron, and appears to be formed from haemoglobin.

An abnormal condition of the liver, by leading to excessive destruction of blood-corpuscles, may therefore be an important cause of anaemia. The corpuscles contain albuminous matters as well as haemoglobin, and deficiency of albumen in the blood will lead to anaemia. Thus, in cases of Bright's disease, the loss of albumen through the kidneys tends to produce anaemia, and this must be combated by lessening the loss, if possible, as well as by supplying albumen.

The blood-corpuscles also contain fat, and deficiency of fatty food will tend to produce anaemia. Cod-liver oil, on the other hand, which is an easily assimilated form of fat, is a powerful haematinic. In anaemia there is a deficiency of iron in the blood, and chalybeate preparations are among the most powerful of all haematinics.

One well-marked disease due to imperfect nutrition is scurvy. In it there is not only a deficiency of red blood-corpuscles, but a tendency to extravasation. Its pathology is not definitely made out, and it has been supposed to be due to a deficiency of salts of potassium in the blood, but it is much more likely that it is due to increase in the chlorides, and especially chloride of sodium, either absolutely or relatively to the carbonates.

Excess of chloride of sodium causes the blood-corpuscles to pass out of the vessels (p. 63), and potassium salts alone, or beef-tea, which contains them, do not cure scurvy; but it is removed by fresh vegetables or by lime-juice.