When less perfectly purified, the sulphur has amounted to 60 grains in 100 cubic feet, which is thrice the maximum allowed by Act of Parliament; carbonic oxide, 11 per cent.; marsh-gas, 56 per cent.; besides a great number of hydrocarbons and alcohols and other chemical compounds in small amount.

The products of combustion vary much with the quality of the gas and the completeness of the process, but 100 cubic feet will unite with from 90 to 164 cubic feet of oxygen, and produce 200 cubic feet of carbonic acid and from 20 to 50 grains of sulphuric acid, so that 100 cubic feet of coal gas consume the oxygen or destroy the vital qualities of 800 cubic feet of air, and raise the temperature of 31 290 cubic feet of air 100° Fahr.

With imperfect combustion, 67 per cent. of nitrogen, 16 per cent. of water, 7 per cent. of carbonic acid, and 5 to 6 per cent. of carbonic oxide, with sulphurous acid and ammonia, are thrown into the atmosphere, but the quantity of carbonic acid will be materially reduced with more perfect combustion. Only a very imperfect appreciation of the effect of gaslighting on the air respired at present exists, but if the

products above mentioned are allowed to escape into the room, whilst at the same time the air is thus robbed of its oxygen, the slightest reflection will suffice to show how unfit such air must be for the respiration of man. Such is almost invariably the practice, but it is possible by the use of ventilating gaseliers to remove all the products from the room, and to supply pure air at the same time.

FLOATING PARTICLES.

The floating particles in the atmosphere may be readily collected by the aid of cotton wool placed in a glass tube, and air aspired through it, and, when collected, may be examined with the microscope. Dr. Smith found a great variety of substances, animal, vegetable, and mineral, but it does not thence follow that they were the causes of particular diseases. Such an enquiry should, however, have the germ-theory of disease in view, in order to add to our knowledge, if not to find the immediate cause, of disease. This has, in some degree, been advanced by the theory that scarlet-fever is transmitted by the detached scarf-skin, which may be inhaled or otherwise brought into contact with the body and convey the disease to others.

Dr. Angus Smith found various organisms in crowded rooms with vitiated air. Thus he writes :—

I mentioned some time ago that I had got a quantity of organic matter from the windows of a crowded room, and I have since frequently repeated the experiment. This matter condenses on the glass and walls in cold weather, and may be taken up by means of a pipette. If allowed to stand some time, it forms a thick, apparently glutinous mass; but when this is examined by a microscope, it is seen to be a clearly marked confervoid growth.

SECTION VI.

METEOROLOGICAL AND SEASONAL

INFLUENCES.*

Nothing is better established than the fact that the mortality from various diseases varies with meteorological and seasonal conditions, and that at certain periods one class of diseases may be expected to prevail, and at other periods other diseases. So certain is this relationship that an excess of the seasonal conditions, whether of heat in summer or of cold in winter, increases the mortality, while a mild season as it is called, viz. a cool summer and a warm winter, is attended by a diminution in the deaths due to seasonal influences.

This influence is not restricted to this country or to our own day, but has existed in all countries and ages, and is as clearly admitted in the writings of the ancients as in the mere matter-of-fact reports of our Registrar-General.

I propose on this subject to extract some remarks from my work on cyclical or periodical influences,† which will sufficiently illustrate the subject.

STATEMENTS OF THE ANCIENTS.

255. It is almost impossible to turn over the pages of the medical fathers without finding how much importance was attached to season in the production and cure of disease, or without admitting that the information which they have handed down to us is true and applicable to our own era. We do not purpose to enter at any length into the history of this department of knowledge; but we think that it will be

* See also "Climate," page 72.

Health and Disease: Periodical Changes in the Human System; King & Co., Cornhill.

instructive to notice with what extent and accuracy the influence of season was known to Hippocrates, as is shown in the twenty-four Aphorisms which he has transmitted, and which have been so ably edited for us by Sprengel,* Adams, and Clifton.

256. The division of the seasons has varied with different nations and eras, and has been arbitrary, except so far as it was associated with the occurrence of certain natural phenomena more or less general or peculiar to the locality. We find that in the most ancient periods the Egyptians + divided the year into three seasons, viz. the "Season of Vegetation," the "Season of Manifestation," and the "Season of the Waters,” or the “Inundation;” and at the present time the first is called "Winter,” the second “Summer," and the third “Inundation," or literally "The Nile." This division was associated with terrestrial changes; but in ancient Greece it was determined by astronomical phenomena, as it is with us at the present day.

257. Dr. Adams informs us that with the ancients Winter began at the setting of the Pleiades, viz. the period when they set with the sun, and continued to the vernal equinox. Spring commenced at the last-mentioned period (the vernal equinox), and ended at the rising of the Pleiades, viz. the rising with the sun. Summer began at the rising of the Pleiades, and continued to the rising of Arcturus; and Autumn extended from the rising of Arcturus to the setting of the Pleiades. Thus the division of the seasons was purely astronomical, and the constellations of the Pleiades and Orion were the dividing objects; the rising of the Pleiades with the sun separating the first from the second half of the year, and the setting of the same constellation with the sun terminating the year.

258. Having thus defined the several seasons, we will now, in a few words, give a condensed account of their influence as gathered from the opinions of Hippocrates, expressed in the Aphorisms above mentioned.

259. Change of seasons and the alternations of cold and heat in those seasons are most effectual causes of diseases.

*Aphorisms of Hippocrates, by Dr. Sprengel; London, 1708. † Hora Egyptiaca, 1851.

Some natures are well or ill affected in summer, and some in winter. Some diseases and some ages are well or ill affected at different times of the year, &c.

260. Autumnal diseases may be reasonably expected when on the same day it is sometimes hot and sometimes cold. The south wind dulls the senses of hearing and sight, causes headache, heaviness, and faintness. When it prevails, these incidents occur to the weak and sickly. The north wind affects the chest and throat, and causes constipation, dysuria, and muscular pains. The south wind relaxes and the north wind contracts the tissues of the body. When the summer is like the spring (viz. cool and wet), we must expect much sweating in fevers. Dry seasons are the cause of sharp fevers.

261. Constant and seasonable times of the year are accompanied by diseases which are regular and mild, but in inconstant and unseasonable times the diseases are uncertain and difficult of cure.

262. In autumn diseases are most acute and pernicious, and that season is hurtful to those in consumption. Spring is most healthy and free from fatal disease. If the spring be rainy with southerly winds, and have followed a dry and cold winter, there will be in the following summer acute fevers, catarrhs, and bloody discharges. With a dry and northerly spring, following a rainy and warm winter, there will be bloody discharges, ophthalmia, rheumatism, and catarrhs, fatal to old people. Abortions easily arise under these conditions, and children thus born near the spring are weak and diseased, and either grow up so or die quickly. A rainy and warm (southerly) autumn, following a dry and cold (northerly) summer, will produce in the winter pains in the head, cough, catarrhs, and consumption. A dry and cool (northerly) autumn is good for those of a moist temperament, but to others it produces ophthalmia, acute and lingering fevers, and melancholy.

263. Great droughts are more wholesome and less destructive than continual rains and frequent showers. Continual rains cause most diseases, as lingering fevers, diarrhoea, diseased humours, falling sickness, and apoplexy. Great droughts occasion consumption, inflammation of the eyes, rheumatism, incontinence of the urine, and bloody discharges. 264. Continued northerly weather braces and strengthens