In many instances the marshy country itself may be made salubrious, and this has been done on a large scale all over the world; Lower Egypt is one of the most remarkable instances of this. Lower Egypt used to be most fertile and prosperous - it was the place from which all the arts and sciences originated, the place in which medicine was first cultivated, and in which attention was first given to sanitary science. Moses, who was "learned in all the wisdom of the Egyptians," gave us the most admirable code of sanitary laws ever issued. Lower Egypt was the place, indeed, from which started all our knowledge; a highly intellectual race inhabited it at one time. Later on, through neglect of drainage, it became the most pestilential swamp, the home of the plague, which ravaged the whole world.

Intermittent fevers used to be much more fatal in England than they are now. The Registrar-general, I see in his summary for ten years, draws attention to this fact, which is the result of increased drainage of soil, so that there is no doubt whatever, that by drainage, the death-rate from marshy diseases may be lessened to a very considerable extent.

I said that, according to Humboldt, height above the sea was the most important fact as regards the climate of a place, and the higher the place above the sea, the lower its temperature, until at last we get to the region of perpetual snow. You think it is a strange thing that the higher and nearer to the sun we get, the more the temperature is lowered, but the reason is that the air is so rare that it does not absorb the sun's rays; they pass through it. The higher you go the rarer the air is, and so each time you breathe you breathe in the same volume but less weight of air, and therefore less weight of oxygen, so in order to get the amount of oxygen which is required for the purposes of the system you have to breathe more times, and people who live high above the sea level always breathe more quickly, hence those who require their lungs exercised adopt the excellent plan of going up into the mountains.

The diseases prevalent in mountainous countries are those due to cold, such as lung diseases, rheumatism, and heart disease consequent on rheumatic fever, but they are more specially prevalent, not in exposed situations but in gorges and valleys, where the air is stagnant and damp: cholera and typhoid fever are rare in mountainous countries, and in many such places cholera has never appeared at all.

Cold, then, is an important consideration, and this leads me to say that things made of wool are warmer, because they allow less heat to get away from the body, and another reason is that they absorb the moisture of the shin much more readily than clothes made of cotton or linen.

Land which is covered with vegetation, other things being equal, is colder and moister than dry places, for we know that dry places when there is no vegetation at all are some of the hottest places in the world, as, for instance, the desert of Sahara.

A word or two about the condition of the soil itself. Soils may be divided roughly into pervious soils and impervious soils. Places built upon pervious soils such as gravel, sand, chalk, through which the water can penetrate are dry, and generally healthy: lung diseases, rheumatic diseases; and consumption, are less prevalent there. The diseases that are prevalent there are cholera and typhoid fever; they spread upon these soils, according to the theory of a great German hygienist, on account of the emanations which are given out of these soils under certain circumstances, but in England we believe that these diseases spread because people drink water from wells in the soil into which impurities have percolated.

Upon impervious soils the disease that is especially prevalent is consumption, and on all undrained soils, whether pervious or impervious, this disease, the plague of temperate climates, is prevalent. Dr. Buchanan has shown that there are no instances among the cases investigated, where the level of the water in the soil beneath the houses has been lowered by drainage, in which the death-rate from consumption has not been lessened, and in one town in England it was lessened fifty per cent. Various lung diseases and rheumatic affections are also prevalent on damp soils. It is exceedingly important that we should live upon dry soils, and there should be in every house what is called a damp course, a little distance above the ground all round the wall, of asphalte or glazed stoneware, so that the moisture cannot rise up through the walls. It is very important, too, that the basement of all houses should be impervious to water; there should be a layer of asphalte or concrete, all over the basement floor, above which the boards should be laid, and, if possible, there should be a ventilated air-space between the floor and the asphalte or concrete, so that no damp can rise up into the house; another reason for that is, that all soils contain a certain amount of air; pervious soils contain a good deal, and that is air which should not be admitted into the house, as it contains a large amount of moisture and organic matter, which may be very foul.