Page:Popular Science Monthly Volume 24.djvu/148

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138
THE POPULAR SCIENCE MONTHLY.

size, and a palatable, fleshy, smooth-skinned covering like plum. The nut affords an oil, which solidifies under a slight decrease of temperature, and is used throughout North Africa as a substitute for butter. The Parkia biglobosa (runno-kau) of the same region, a leguminous plant, furnishes an excellent food in its seeds, which are eatable while still unripe. The ripe seeds contain a thick, saffron-colored marrow inclosing black, shining grains. The meal made from them forms when mixed with water or milk a pap, which has a sweet and pleasant taste at first, but soon cloys. Relieved with sour milk or tamarind-juice, it forms a dish healthful and enjoyable to all. The wool-tree (Eriodendron anfractuosum) is the third characteristic tree of the country. It rises straight up, with thick, horizontal branches arranged in whorls one above the other, and derives its name from its fruit, which bursts like the pods of cotton and discloses a similar mass of fibers, lustrous and soft as eider-down. This "wool" is used for the stuffing of cushions and mattresses and for the wadding-armor of the heavy cavalry. It has the valuable property of never becoming so compact but that it can be restored to its original volume by a short exposure to the sun. The tree is a favorite place of refuge for the negroes in time of danger. Taking their children and goods up with them, they secure an excellent natural fortress among the whorls of its limbs.

 

Disposition of Sewage.—Professor Henry Robinson remarks, in a paper on "Home Sanitation and Sewage Disposal," that the latter question should be regarded as involving a combination of sanitary and agricultural interests, of which the first is paramount and the latter should be disregarded when incompatible with it. Sewage is purified in passing through the soil by one or more of three processes: 1. By simple filtration or removal of the suspended matter; 2. By the precipitation and retention, in the soil, of ammonia and various organic substances previously in solution; and, 3. The oxidation of ammonia and of organic matter with the aid of living organisms. A filter-bed may be constructed so as to have a greater oxidizing power than would be possessed by ordinary soil and subsoil, by laying over a system of drain-pipes a few feet of soil obtained from the surface of a good field, care being taken to select a soil containing a considerable amount of carbonate of lime and organic matter. Such a filter-bed would be far more porous than a natural soil and subsoil, and would possess active oxidiizng functions throughout its whole depth. The presence of antiseptics interferes with the fermentation, and refuse from chemical works hinders the progress of purification. Much valuable information has been published by Drs. Lawes and Gilbert on the chemical changes that take place in the soil under varying circumstances; and Dr. Angus Smith, a rivers pollution inspector, has much to say in his last annual report on the action of air on sewage and the mode of treating sewage so as to hasten aeration; while in a previous report he has discussed the treatment of sewage by chemicals. Much information on these subjects may also be found in Mrs. Robinson's work on "Sewage Disposal" (Spon, London). Well-adapted lands have been found capable of purifying the sewage of about five hundred people per acre. The average amount disposed of in nineteen towns where broad irrigation was practiced was equivalent to the sewage of one hundred and thirty-seven people per acre.

 

Communicability of Disease by Food.—Except the diseases associated with tape-worm and trichinæ, the only animal diseases which there is or has been ground for regarding as transmissible to man, through ingested meat, are cattle-plague, swine-typhoid, epizoötic pleuro-pneumonia, foot-and-mouth disease, anthrax and anthracoid diseases, crysipelas, and tuberculosis. Mr. Francis Vacher, medical officer, of Birkenhead, England, having examined the evidence in respect to the communicability of these seven diseases, has announced the conclusion, in the "Sanitary Record," that only two of them—foot-and-mouth disease and anthrax—can as yet be pronounced communicable to man by infected flesh, while the communicability of the others, although it can not be positively denied, remains unproved. Cattle-plague has been supposed to be allied to various forms of human disease, but