Some substances are decomposed while passing out of the body. Decomposing matters in the intestines and in the saliva, cause the formation of Sulphuret of Iron, while chaly-beates are taken, which blackens the fæces; and of Sulphuret of Lead, when lead is taken for some time, producing the well known blue line on the gums.
Changes of Reconstruction.—The elements of a body may be disturbed in the system, and combined together anew, without any material or apparent alteration of its properties. Probably many changes of this kind occur, but only some isolated instances have been verified. Thus Tannic acid, acquiring Oxygen, changes into Gallic. Benzoic and Cinnamic acids are converted into Hippuric acid, which passes out in the urine. Turpentine changes into a volatile oil, which communicates to the urine an odour of violets. Ferridcyanide of Potassium changes in the system into Ferrocyanide. Some of these changes will be afterwards considered more at length.
Changes of decomposition.—By this I mean such a disarrangement of elements as shall neutralize or reverse the action of a medicine.
There is free Oxygen in the blood, and the most important change to which all organic substances are liable there is oxidation.
This probably occurs in many cases. It always takes place with the starchy elements of the food, and with those parts of the nitrogenous tissues that have done their work, and are preparing to be excreted from the body.
By this oxidation Wöhler has proved that the alkaline salts with vegetable acids are changed in the blood into alkaline carbonates. From being first neutral, they become now alkaline in their reaction, and affect the urine in the same way as free alkalies.
(Vide Hæmatics, ord. Acida, Alkalia, Tonica, Solventia.)
We have now to treat of the actions of medicines in the blood. These are recited in the four remaining Propositions.
The seventh treats of Hæmatics, acting primarily in the blood.