The absorbent system is distributed over every part of the body. In the brain alone the vessels of this class have not, hitherto, been detected and submitted to ocular demonstration by any other anatomist than Mascagni. But physiological and pathological proofs of their existence, equal in force to any anatomical evidence, are not wanting to demonstrate their presence in the central organ of the nervous system. The office which these vessels discharge, in the nutrition of the body and removal of its waste, is most important to its healthy condition; and the influence it exerts, in a state of disease, is not less considerable. From the inactivity or obstruction of the absorbent vessels, a great proportion of the chronic disorders of the body take their rise. Medicines, therefore, which act either directly or indirectly on this system, have always been accounted most valuable articles of the materia medica. Unhappily, they too often deceive us in their operation, and, notwithstanding the united studies of many physicians directed to them, the causes of their failure, as well as the circumstances under which they succeed, still remain a problem. A considerable step towards the solution of this difficulty has, indeed, been lately taken by Dr. Blackall. Much obscurity, however, yet rests upon the subject, and a direct medical agent on the absorbent system, whose effects are speedy, indubitable, and powerful, is a great desideratum in the art of healing. Such an agent is iodine. Its effects on the absorbent system are incontrovertible. They are as speedy as they are certain, and so powerful are they, that if the medicine be not duly and cautiously managed, we have already seen what havoc may be the result. A few, a very few, cases have occurred to myself, in which the constitution was altogether insensible to its action; I believe a greater number have occurred to others; but I cannot help thinking that such cases have been owing, in many instances, either to some fault in the medicine, or to some inadvertence on the part of the practitioner.[4] [4] The iodine which is sold in the shops is of very different degrees of purity, which will probably afford an explanation of some of the above anomalies. But still after all possible care has been taken, there will be found a few instances in which it does not appear to possess any power over the absorbent system.