460 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 nohilis 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 cenomani- 

 enne chalk of Bohemia, the Hedera priniordialis, 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 Philihertii, 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 Al- 

 giers, 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 acutelohata 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 knowl- 

 edge 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 agree- 

 able as it is instructive. — Hevue Scientijique. 



HOW TYPHOID FEYER IS CONYEYED. 



By De. 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 preva- 

 lent on the Continent. 



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



