Page:Popular Science Monthly Volume 11.djvu/262

250 mass of the population have to deny themselves this wholesome form of nutriment. The London Society of Arts has undertaken the investigation of the question of fruit-growing, and is laboring to awaken a popular interest in the matter. In this country fruit is cheap and abundant, yet many of the suggestions made on the other side of the Atlantic would not be out of place even here. In one of the papers read before the Society of Arts, it is stated that only 40,000 acres of land are set apart in England for market-gardens. Considering what enormous crops of fruit are obtained from this inconsiderable acreage, how shall we estimate the product of waste lands were they to be cultivated? The market-gardens, as we have seen, cover less than 60 square miles; but the railway embankments represent about 200 square miles of land, one-third of which, at least, could be used for the cultivation of fruit. The little plots of ground attached to cottages in the country and in villages and suburban districts might also be utilized for fruit-growing. Roadsides in the country might also be cultivated profitably. The prospect of success in this effort at enlarging the area of fruit-culture in England is not very encouraging, owing to the unthriftiness of the people. In this respect they compare very unfavorably with their neighbors, the French.

Frequency of Color-Blindness.—There is some reason for believing that writers on "color-blindness" have in many instances exaggerated with regard to the frequency of its occurrence. Thus it has been stated as a fact that no less than ten per cent, of the railroad engine-drivers in Sweden are unable to announce properly the color of the signal-lamps, owing to color-blindness. Mr. Herbert W. Page, surgeon to the London and Northwestern Railway, is of the opinion that, so far from being common, this affection is extremely rare. He cites the testimony of three railway examining surgeons in support of his views. One of these, who in the course of twenty-five years had examined many hundreds of men, writes that color-blindness "is of excessive rarity;" another "has not found it common;" while a third, a surgeon of long experience, writes that he has met with "only three cases of well-marked color-blindness" among many hundreds examined by him. In 800 men examined by Mr. Page himself, not one instance of true color-blindness was found. Similar testimony is given by Dr. Macaldin, of the Midland Railway.

How, then, are we to account for the positive statements of other writers who assert the extreme frequency of this affection? In very many cases ignorance of the names of colors is, doubtless, mistaken for inability to distinguish between colors themselves. Then, many persons are hesitating and slow in their recognition of colors. "Green may be spoken of as blue by one, red as green by another, and the name persisted in till the man be asked to compare the one before him with some familiar color, as the grass or sky, when his mistake will be recognized at once. I cannot help thinking," adds Mr. Page, "that such cases as these have often been mistaken as instances of color-blindness. It certainly is within my own experience, that errors of this kind may creep in unawares unless time and care he given to the examination of those who are ignorant stupid, or nervous."

Marsh-Fevers.—A substantial addition to our knowledge of the true nature of paludic fevers appears to have been made by Messrs. Lanzi and Terrigi, of Rome. Lanzi has found in the cells of microscopic algæ from the Roman marshes certain dark-green granules, which are most numerous when the plants are farthest gone in decomposition. At length these granules fill the cells, are black under the microscope, and the algae emit an offensive odor. In the Campagna marshes are formed in winter, which in spring develop algae abundantly. In summer the water disappears, and the algae then putrefy, the ground afterward growing phanerogamous plants. Toward the fall of the year the algae in the parts still covered with water also die, and the slime at the bottom of the marshes contains quantities of the dark granules. The latter may also arise from other plants in the state of decay, even where there are no marshes. Lanzi regards these granules as a sort of ferments. Now, the pigment-granules found in the liver and spleen of individuals suffering from malaria have quite similar properties to