. A text-book upon the pathogenic Bacteria and Protozoa for students of medicine and physicians. Bacteriology; Pathogenic bacteria; Protozoa. The Plague Fleas 601 five to ten days, a minute, active, caterpillar-like larva emerges from the egg to feed upon such organic matter as it may find for the six to eight weeks of this stage. During the larval period the skin is shed three or four times. When full grown, the larva empties its alimentary canal, spins itself a tiny silken cocoon, sometimes including minute bits of rubbish or grains of sand in its structure, sheds its skin for the last time,
. A text-book upon the pathogenic Bacteria and Protozoa for students of medicine and physicians. Bacteriology; Pathogenic bacteria; Protozoa. The Plague Fleas 601 five to ten days, a minute, active, caterpillar-like larva emerges from the egg to feed upon such organic matter as it may find for the six to eight weeks of this stage. During the larval period the skin is shed three or four times. When full grown, the larva empties its alimentary canal, spins itself a tiny silken cocoon, sometimes including minute bits of rubbish or grains of sand in its structure, sheds its skin for the last time, and becomes a pupa. As such it is inactive for from two to eight weeks, according to external conditions of temperature and moisture, then opens the cocoon and emerges from the pupa shell, a perfect in- sect—the flea proper. The adult fleas, both males and females, have soft exoskeletons at first, but soon they harden, through the formation of chitin, to the well-known tough and brittle Fig. 239.—Various fleas, magnified about 30 diameters. The specimens are treated with hot 20 per cent, caustic potash for a few minutes, dehydrated in alcohol, cleared in xylol and mounted in balsam, a, Ctenocephalus canis, cf; 6, Ctenocephalus canis, 9; c, Ctenocephalus felis, &; d, Ctenocephalus felis, 9 (Bacot, in Journal of Hygiene, "Plague Supplement in, 1914"). The male differs from the female in being smaller and in its shorter abdomen. Both insects hop about in search of the appropriate warm-blooded hosts upon whose blood they are to live. Each kind of flea has a preferred host, but the tastes of all are more or less cosmopolitan, so that in the absence of the preferred host, another kind of warm-blooded creature wiU do. Adult fleas live solely by sucking blood. The longevity of a flea varies according to conditions of temperature and mois- ture. Life is longest when the temperature is high and the ground not too dry. They may live for months without feeding; w
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbacteri, bookyear1919
