storms in our temperate climate, is accompanied by an increase in the various odours perceived in the air. The perfume of flowers is very much stronger for awhile; and, in country places, it is not unusual to perceive, at such times, the disagreeable odour of cess-pools all over the district-a fact which clearly points to the necessity of a more perfect system of drainage and disinfection in our country homes.

CHAPTER X.

An Unexplained Condition of the Atmosphere-Effects of Glare— Snow-blindness-Hemeralopia and Amaurosis.

THERE is a certain, hitherto unexplained, condition of the atmosphere, which usually lasts for a few hours at a time, and rarely more than one day, or, perhaps, two days. During this condition the optic nerves of men and animals are painfully affected. I allude to what is commonly called "glare," not unfrequently perceived at the seaside, and often when the sun is not shining brilliantly, but is hidden by thin cloud, or haze.

The existence of this painful "glare," even when the sun is dimmed, is a subject which has not been fully studied. I feel convinced that we have in the solar spectrum, besides the rays of light and heat, and the actinic, or chemical rays, others which specially affect the nervous system in the higher animals, and which appear to act also on those lower forms of life, in some of which no traces of a nervous system have, as yet, been discovered. This peculiar condition of the atmosphere affects some people more than others. Many are obliged to wear coloured glasses

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in order to avoid its effects, or to pull down the brim of their felt hats to a level with the lower eyelids, as they do at Naples.

Snow-blindness is supposed to be occasioned by the vivid reflection of the solar light from the white mantle of the brilliant white crystals which covers the ground, and more or less complete amaurosis is produced, especially in aged persons, by the bright solar radiation on the sea-coast, or by the light from brilliant white houses in inland cities.

One of the most remarkable cases of snow-blindness ever reported is that by the late General Miller, in the Edinburgh New Philosophical Journal (1835): A division marching from Cuzco to Puno, in Peru, halted at Santa Rosa. During the night, snow fell abundantly, nevertheless the march was continued next day, when, with few exceptions, the whole of the soldiers were attacked with sore eyes, “due to a disease called by the natives norumpi. It produces almost total blindness for some time, and great pain. There is also delirium of a peculiar kind, and it is often fatal. The division in question lost one hundred men in fifteen hours from this affection. The disease generally lasts two days."

Dr. August Berlin, of Stockholm, has proposed a new theory for snow-blindness. He went on an expedition to Greenland in 1883, during which he had ample opportunities for observing it.

The geographical distribution of the affection closely follows the isothermal lines in the three continents

bordering on the North Pole; it comes further south in America and Asia than it does in Europe. It is also met with in very elevated regions, even under the tropics. In the temperate zone it occurs occasionally, but in a milder form. Its cause, according to Dr. Berlin, resides in great dryness of the air, and intensity of the solar rays.

To prevent snow-blindness the Esquimaux use a disk of thin wood with a minute transverse slit in the centre. They call these wooden spectacles their "snoweyes." Instead of this, goggles made of moderately fine wire network, without glass, have been recommended.

Medical men class these atmospheric effects upon the optic nerve under the term of hemeralopia (or "nightblindness," because they are chiefly observed at night). It is not uncommon that a considerable number of soldiers become thus completely blind during the night, and recover their sight again at daybreak. The complaint comes on periodically every evening, and may last for a fortnight, or even for a whole month, when it disappears without leaving any traces.

The army surgeon, Dr. Hetter, saw sixty of his men struck down in this way at Wissembourg, just before the Franco-Prussian war; and the troops in garrison at Strassburg suffered in a similar manner. Generally speaking it is cured, in mild cases, by keeping the men in the dark for two or three hours; or, sometimes, for twelve hours. In 1891, Dr. Schirmer endeavoured to explain this extraordinary atmospheric effect upon the

eyes, by reporting it to an action upon the pigmentcells of the retina. But it still remains a mystery. That same year Dr. Venneman described an “epidemic” of hemeralopia which he observed in the neighbourhood of Louvain (Belgium). Forty-two cases of this peculiar affection came under his observation, and embraced all classes of people, children being more generally affected than adults. Fever, with headache, preceded the affection of the eyes, and lasted for two or three days. With the appearance of these symptoms the ophthalmoscope revealed a slight retinal oedema about the disc, especially along the course of the vessels, with diffuse streaks and markings of black pigment. When normal vision returned these appearances gradually vanished.

It is, therefore, an atmospheric effect upon the retina, or optic nerve; but no one has yet been able to determine in what consists the special condition of our atmosphere which produces these curious and painful effects. So little does the last-named physician suspect the real cause, that he looks upon the cases at Louvain as an epidemic, similar to influenza, confusing it with the amaurosis so often noticed, of late years, after attacks of that disease.