From a number of experiments made by Dr. Blake, he concluded that when inorganic salts were injected directly into the circulation, the intensity of their physiological action increased in proportion to their molecular weight, but only in those groups of elements where the salts were isomorphic, or in other words, crystallised in the same forms. Thus groups whose salts were crystallised in different forms had quite different physiological actions. He adopts Mitscherlich's division of the elements into nine groups, and considers that the physiological action of the different groups differs in kind, whilst that of the individual members of the same group agrees in kind but differs in degree. Thus he states 1 that the salts of the first group increase in activity in the order mentioned, silver being the most active, and lithium the least.

1 Blake, American Journal of Science and Arts, vol. vii., March 1874 (corrected reprint).

These groups are as follows :Group 1. Lithium, sodium, rubidium, thallium, caesium, and silver. According to him they produce death by acting on the lungs and impeding the pulmonary circulation. None of them affect the nervous system excepting caesium; nor do any affect the pulmonary circulation excepting silver.

Group 2. Magnesia, ferrous salts, manganous salts, nickel, cobalt,copper, zinc, and cadmium are increasingly lethal in the order mentioned. They kill by arresting the action of the heart.

Group 3. Beryllium, alumina, yttria, cerium, and ferric salts both impede the systemic and pulmonary circulation.

Group 4. Calcium, strontium, barium, and lead salts kill by paralysing the ventricles of the heart.

Group 5. Palladium, platinum, osmium, and iridium act on the heart, respiration, circulation, and blood.

Group 6. Ammonia and potash paralyse the heart and cause convulsions.

Group 7. Hydrochloric, hydriodic, bromic, and iodic acids impede the circulation and kill by arresting the circulation.

Group 8. Phosphoric acid, arsenic acid, and antimony kill by arresting the pulmonary circulation.

Group 9. Sulphuric and selenic acid impede the pulmonary circulation.

The author's statements regarding the mode of action of the elements show that their physiological action has not been fully investigated, and his results as to the lethal dose are probably only approximate and may want re-investigation; but while we cannot accept at present all his results or conclusions as final, yet his last and chief conclusion is one of great interest - viz., that in living matter we possess a reagent capable of aiding us in our investigations on the molecular properties of substances.