Looking first at these upper lines, we notice two interesting facts. The first is, the large and steady improvement of both forces as regards health-conditions during the thirty-five years; and the second is the considerable and constant difference in the disease mortality of the two services, the soldiers having throughout the whole period a much higher mortality than the sailors. The decrease of the general mortality is clearly due to the great improvements that have been effected in diet, in ventilation, and in general health-conditions; while the difference in health between the two forces is almost certainly due to two causes, the most important being that the sailors spend the greater part of every day in the open-air, and in air of the maximum purity and health-giving properties, that of the open sea; while soldiers live mostly in camps or barracks, often in the vicinity of large towns, and in a more or less impure atmosphere. The other difference is that soldiers are constantly subject to temptations and resulting disease, from which sailors while afloat are wholly free. Turning now to the lower lines, we see that, as regards small-pox mortality, the Navy suffered most down to 1880, but that since that period the Army has had rather the higher mortality. This has been held to be due to the less perfect vaccination of the Navy in the earlier period, but of that there is no proof, while there is evidence as to the causes of the improvement in general health. Staff-Surgeon T. J. Preston, R.N., stated them thus: “Shorter sea-voyages; greater care not to overcrowd; plentiful and frequent supplies of fresh food; the introduction of condensed water; and the care that is now taken in the general economy and hygiene of the vessels” (Q. 3,253). These seem sufficient to have produced also the comparative improvement in small-pox mortality, especially as the shorter voyages would enable the patients to be soon isolated on shore. The question we now have to consider is, whether the amount of small-pox here shown to exist in both Army and Navy demonstrates the “full security” that revaccination is alleged to give; whether as a matter of fact our soldiers and sailors, when exposed to the contagion of intense small-pox, _do_ suffer to “any appreciable degree”; and lastly, whether they show any immunity whatever when compared with similar populations who have been either very partially or not at all revaccinated. It is not easy to find a fairly comparable population, but after due consideration it seems to me that Ireland will be the best available, as the statistics are given in the Commissioners’ Reports, and it can hardly be contended that it has any special advantages over our soldiers and sailors,—rather the other way. I have therefore given a diagram, XII., in which a dotted line shows the small-pox mortality of the Irish people of the ages 15 to 45 in comparison with the Army and the Navy mortality for the same years.