They also increase the number of leucocytes in the blood, and the more irritating of them increase the flow of blood to the pelvic organs, and may thus stimulate the uterus, or in large doses cause abortion.
The methods of research are essentially those employed by physiologists, the action of substances being studied in the usual way on bacteria, leucocytes, frogs, rabbits and other animals.
Recent researches on arsenic and atropine, however, point to the leucocytes as playing an important part in the production of tolerance, as these gradually become capable of ingesting large amounts of the foreign substances, and thus render them more or less harmless to the tissues, until they are gradually excreted from the body.
When the amount is too large to be dealt with by the leucocytes, poisoning seems to occur even in the most habituated.
Hence quinine stops the process of diapedesis or emigration of the leucocytes from the blood-vessels into the tissues, and if applied to the, extravascular spaces it arrests the leucocytic movements there.