Page:Popular Science Monthly Volume 7.djvu/136

126 constitutes, as is superficially said, a toxic element. The phenomenon is more complex. The organic matter in suspension or in solution creates in the water a peculiar medium, suitable for the development of exceedingly small beings of the genus Vibrio. It is no longer mere water—it is a world of microscopic animals and plants which are born, live, and increase with bewildering rapidity. The infusoria find in the water calcareous, magnesian, and ammoniacal salts, and their maintenance is thus secure. Drink a drop of this liquid, and you swallow millions of minute beings. But there are vibrios and vibrios. There are those which are capable of setting up putrefaction in our tissues. These are our enemies, often our mortal enemies. Let water be placed in contact with organic remains capable of nourishing these malignant vibrios, and it at once becomes more dangerous than any poison."

A Motherly Fish.—There is found, in the clear, pebbly streams which descend to the plains from the mountain-ranges of Trinidad, a small fish of the perch tribe, which in its great care for its young presents a singular contrast to all other known fishes. A writer in Nature states that on one occasion, as he approached the water for the purpose of taking his morning bath, his attention was attracted by the eccentric movements of one of these little fishes. In general they are very shy, scudding off into deep water on the approach of man; now, however, when a hand was put into the water, the fish darted forward again and again, striking the hand with considerable force. The explanation of this conduct was soon found: in a small hollow near by, about the size of half an egg, artistically excavated in the bright quartz-sand, a multitude of tiny fish were seen huddled together. They had apparently been very recently hatched, and were no larger than common house-flies; the parent-fish kept jealous watch over her progeny, resenting every attempt to touch them. Returning to the same spot on the following day, the writer of this narrative searched there in vain for the fish and her young. At length, however, a few yards farther up stream the parent was discovered guarding her fry with zealous care in a cavity similarly scooped out in the coarse sand; any attempt to introduce one's finger into the nest was vigorously opposed by the watchful mother.

Arsenical Colors.—A Swedish chemist, Dr. Hamberg, has made some important researches on the arsenical coloring-matters of wall-paper. The paper of the room in which the experiments were conducted had a light-green ground, with an ornamental pattern of brownish-yellow color; this yellow was probably derived from an ochre, but the green resembled Schweinfurt green, and was strongly arsenical. An arrangement was made for drawing a current of air through a series of U-shaped and bulbed tubes, suspended on the wall. The passage of air was continued from July 16th to August 16th, and it was calculated that during this time about 2,160,000 cubic centimetres of air had traversed the system of tubes. Some of the tubes had been plugged with cotton-wool, while others contained a solution of nitrate of silver, and at the termination of the experiment the contents of the tubes were separately examined. The results showed that there had been an arsenical exhalation. The family living in the house had never suffered any marked injury from breathing this I poisoned air; but Dr. Hamberg, after sleeping in a room by the side of the apartment in which his experiments were made, and with the door open, frequently experienced, on the following morning, a sense of heaviness in the head, and a general feeling of weariness.

Distribution of Water in Aquaria.—In constructing aquaria it is important to bear in mind the fact that, for aquatic animals which breathe without lungs, the value of water does not depend so much on its amount, as upon its distribution in such a manner that it may be sufficiently oxygenated by contact with the atmosphere. Mr. W. A. Lloyd, who calls attention to this matter in the Zoologist, says that when the amount of surface of water exposed to air, as well as the actual quantity of water, is regulated according to the known requirements of the animals to be kept, the well-being of the creatures is promoted, and the