General Action. - In regard to the action on the nervous system of the chlorides of calcium, strontium, barium, beryllium, didymium, erbium, and lanthanum, these substances fall into two groups (a) Containing beryllium, calcium, strontium, and barium;

(b) Containing yttrium, didymium, erbium, and lanthanum.

Group (a) has a tendency to increase reflex action, as evidenced by spasm or tremor in the frog.

With group (b) reflex action in the cord appears to be little affected, but its members appear to have a tendency to paralyse motor centres of the brain in the frog.

Group (a) all paralyse motor nerves to some extent. Lanthanum has also a slight paralysing action, but the other members of the group (b) have not, agreeing in this respect with sodium and rubidium, and differing from all the others.

In regard to their action on muscle these substances cannot be divided into sub-groups. Their action on muscle has been already described (p. 135).

The lethal activity, on frogs, of the chlorides of the alkalies and earths is not in proportion to their atomic weight. It is as follows, potassium being most powerful, and calcium least powerful:- potassium, beryllium, rubidium, barium, ammonium, caesium, lithium, lanthanum, didymium, erbium, strontium, yttrium, sodium, calcium (vide p. 29).

Barium causes contraction of the ventricle of the frog's heart in much the same way as veratrine, and by its local action on the walls of the vessels causes them to contract. When injected into the circulation it causes enormous rise of blood-pressure at first, followed by stoppage of the heart and consequent fall of pressure. It causes contraction also of the involuntary fibres of the bladder and intestine, so that the lumen of the latter may be almost completely obliterated. The symptoms of poisoning in mammals are probably due to its action on the involuntary muscles of the intestines, heart, and vessels, on the voluntary muscles, and on the nervous system. They are vomiting, colic, diarrhoea, muscular weakness and cramp, ringing in the ears, tightness over the heart, and general convulsions. Injection of sulphate of sodium into the veins appears to counteract the effect of barium,1 and the simultaneous injection of potassium salts will prevent death from an otherwise lethal dose of barium.2 The action of barium on muscles and on the heart is abolished by heat in the same way as that of veratrine (p. 128), and the inhabitants of southern climates tolerate much larger doses of barium than those of northern.3

Metals of the Alkaline Earths. Calcium, Strontium, Barium.

The only one of these whose preparations are used internally is calcium. At present barium is only used as a test, though possibly it may yet prove useful in muscular tremor (p. 134).