The city of London has 17,678 persons on a square mile, through its whole extent, including the open spaces, streets, squares, and parks. East London, the densest and most unhealthy district, has 175,816 on a mile. Boston, including East and South Boston, but not Washington Village, has 50,805 on a mile; and the Broad-Street section, densely filled with Irish families, had, when last examined for this purpose, in 1845, a density of population at the rate of 413,000 on the same space. RESULTS OF SANITARY REFORMS. The errors and losses which have been adverted to are not all constant nor universal: not every army is hungry or has bad cookery; not every one encamps in malarious spots, or sleeps in crowded tents, or is cold, wet, or overworked: but, so far as the internal history of military life has been revealed, they have been and are sufficiently frequent to produce a greater depression of force, more sickness, and a higher rate of mortality among the soldiery than are found to exist among civilians. Every failure to meet the natural necessities or wants of the animal body, in respect to food, air, cleanliness, and protection, has, in its own way, and in its due proportion, diminished the power that might otherwise have been created; and every misapplication has again reduced that vital capital which was already at a discount. These first bind the strong man, and then, exposing him to morbific influences, rob him of his health. Perhaps in none of the common affairs of the world do men allow so large a part of the power they raise and the means they gather for any purpose to be lost, before they reach their object and strike their final and effective blow, as the rulers of nations allow to be lost in the gathering and application of human force to the purposes of war. And this is mainly because those rulers do not study and regard the nature and conditions of the living machines with which they operate, and the vital forces that move them, as faithfully as men in civil life study and regard the conditions of the dead machines they use, and the powers of water and steam that propel them, and form their plans accordingly.