Page:Popular Science Monthly Volume 23.djvu/761

Rh , by those who maintain the germ-theory in disease, to atomic germs. The number of disease-germs does not matter, as is evidenced by the communication of disease by letter where the number must necessarily be limited. The atomic dose is but a stimulus to Nature. Nature cures, aided or unaided. The atomic dose but excites in a greater degree those powers of reaction and resistance of Nature already set in motion by disease—which is a disturbing cause. Nature always seeks to restore the equilibrium of her forces.



HE object of this paper is to briefly summarize the present knowledge of the liver-fluke, causing the much-dreaded and fatal "rot" in sheep. Professor A. P. Thomas, of Balliol College, Oxford, has completed his long and extended researches on this parasite, which have been carried on under the direction of the Royal Agricultural Society of England. Professor Thomas's concluding report appeared in the last issue of the "Royal Agricultural Journal," from which the leading facts here given are drawn and the engravings borrowed.

The liver-fluke, shown twice the natural size in Fig. 1, is a sucking-worm related to the common leech, and known to zoölogists as Fasciola hepatica. It has the shape of a privet-leaf, is pale brown or flesh-colored, and from an inch to an inch and a third in length. There is a short projection at one end, and at its tip, y, is a sucking-mouth by which the fluke can attach itself to the surface of the bile-ducts of the sheep. A second sucker, y', is situated at the place where the head joins the body. These flukes are found in abundance in the livers of sheep and other animals infested with the "rot," and produce vast numbers of eggs. Each of these eggs under proper conditions gives rise to an animal "which is never like its parent, never does become like it, and never lives where its parent lives." It will be seen that in the liver-fluke we have an example of what is known among naturalists as an alternation of generations.

The eggs, one of which is shown in Fig. 2 very highly magnified, are about of an inch in length, but may be made visible to the 