Similarly, a host of new and very potent hypnotics have been synthesised in the hope of finding a reliable hypnotic which will not produce a habit, and is perfectly safe. Unfortunately, not much advance has been made in this field. In a few cases impor tant new uses have been discovered for drugs which have been known for many years, such as the discovery in 1918 that quini dine, one of the alkaloids present in Cinchona bark or Jesuit's bark, can cure the important disorder of the heart known as auricular fibrillation. (See CINCHONA, ALKALOIDS oF.) Physiological Features.—The accurate analysis of the mode of action of drugs of well-established reputation has in certain cases greatly increased their value, making it possible to increase their dosage with safety and thus ensuring that sufficient of the drug is given to produce the physiological effect desired. The administration of digitalis in heart disease is a case where con siderable improvements in technique of this character have been effected in recent years.
The study of the actions of extracts of the glands of internal secretion (see ENDOCRINOLOGY) is a field common to physiology and pharmacology. In 1886 it was shown that the two diseases myxoedema and cretinism, due to deficiency of the thyroid secre tion, and previously considered completely incurable, could be cured by the simple remedy of administering dried thyroid gland by the mouth. In 1922 Banting obtained an extract from the pancreas, which he termed insulin (q.v.), and which he proved would relieve the disease of diabetes mellitus (q.v.).
There are peculiar difficulties attending the study of the secre tions of the endocrine glands. Active principles have been obtained from the parathyroid glands and the ovaries which also promise to be of value as agents for substitution therapy, where the normal secretions of these organs are deficient. Substances have been obtained from other endocrine organs which have no certain value as agents for substitution therapy but are drugs with powerful and interesting pharmacological actions. One such sub stance, adrenalin, was discovered in 1896, and has been found of great value in producing constriction of small arteries and thus acting as a haemostatic.
Extracts of the posterior lobe of the pituitary gland produce a rise of blood pressure and constriction of plain muscle and since 1916 this extract has been brought into therapeutic use, and is now very extensively used to cause contraction of the uterus, and thus to accelerate childbirth and to prevent the disastrous complication known as post-partum haemorrhage.
Vitamins.—The vitamins (q.v.) are biological products which have important pharmacological actions. They are unstable bodies of unknown chemical composition which are present in minute amounts in a large variety of fresh foods, but usually are absent in preserved foods. Several vitamins exist, and a regular supply of all of them is essential to normal development and health. Scurvy and rickets are two examples of diseases caused by vitamin lack. Lemon juice has been known for more than a century to be a specific cure for scurvy, and biochemists have now succeeded in concentrating the vitamins of lemon juice so that a child suffering from infantile scurvy can be given the vitamin equivalent of 20 lemons in a single day. Similarly, cod liver oil has long been recognized as a cure for rickets, and the vitamin of cod liver oil has also been prepared in concentrated form.
Parasitology.—The disease-producing parasites are of two classes, firstly the animal parasites such as the trypanosomes, and secondly the vegetable parasites, the bacteria. Very remarkable successes have attended the preparation of internal disinfectants for the animal parasites, and cures have been found for a number of the worst diseases that afflict mankind; in particular, cures have been discovered for a number of very serious tropical diseases (q.v.). Less striking success has attended the endeavour to find disinfectants that will kill bacteria infecting the body, but a cer tain amount of progress has been made, and any advance in this field is of the greatest importance to the inhabitants of temperate climates, because most of the worst infectious diseases of the temperate zone are bacterial in origin.
BIBLIOGRAPHY.—The most important work for general reference is A. Heffter, Handbuch der Experimentelle Pharmakotogie, 3 vol. (1920) ; see also A. R. Cushny, Pharmacology and Therapeutics, 8th ed. (1924) ; W. E. Dixon, Manual of Pharmacology, 6th ed. (1925) ; A. J. Clark, Applied Pharmacology, 2nd ed. (1926) ; T. Sollinann, Man ual of Pharmacology, 3rd ed. Philadelphia, 1926 (bibl.) ; H. H. Meyer and R. Gottlieb, Experimental Pharmacology, 2nd ed. in English, Phila delphia, 1926 (bibl.) ; E. Poulsson, Text-book of Pharmacology and Therapeutics, London, 1923.