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THE POPULAR SCIENCE MONTHLY.

same Laurus primigenia, which at the same time are the most ancient, mark the existence of a race due to the Eocene climate. This influence is gradually lessened, as seen in the expansion of the leaf as we advance toward the Aquitanian, and in the Armissan at first, and Manosque afterward. The relation between the amplified leaves of the Laurus primigenia and those of Laurus Canariensis and Laurus nobilis is more and more pronounced. The Laurus princeps of the superior Miocene approaches still nearer to our laurel; while, finally, the Canarian race has all the characters of Meximieux in the inferior Pliocene.

As to the ivy, its most distant ancestor is a species of the cenomanienne chalk of Bohemia, the Hedera primordialis, whose large leaves bear witness to the moistness of the climate under which it lived. The Pliocene species, Hedera prisca, found at Sezanne, is sensibly removed from the preceding species by the salient angles of its leaves and its much smaller dimensions. The Hedera Philibertii, recently discovered in the gypsum of Aix by Professor Philiberti, testifies clearly, by its narrow and pointed form, to the influence of the Eocene climate. It recalls to our astonishment the most slender forms of the ivy of Algiers, and also the forms that the European ivy takes when it runs on the ground, so that these two races may well have had the Hedera Philibertii for their common point of departure. The Hedera Kargii, characterized by its very small leaves, seems to be derived from the Hedera prisca. The Hedera acutelobata scarcely differs from the actual species; in the same way the Hedera Mac-Cluri is confounded with the ivy of Ireland. Upon the whole, if we consider the varieties presented by our actual ivy we are tempted to believe that the ancient forms have only been races of the same species.

We must here close this analysis. Readers wishing a better knowledge of this important subject than we have been able to give must be referred to the work of M. de Saporta, which will be found as agreeable as it is instructive.—Revue Scientifique.

 

HOW TYPHOID FEVER IS CONVEYED.
By Dr. T. J. MACLAGAN.

TYPHOID fever is one of the most common of the serious ailments of civilized life. No household is safe against it; there is no family which it may not invade. In Great Britain alone not much short of 200,000 people suffer from it every year. Of these nearly 20,000 die, most of them in the prime of life. It is even more prevalent on the Continent.

The question of the contagiousness of such a disease is one of vital