Page:Popular Science Monthly Volume 16.djvu/743

 of inoculating a rabbit with the blood was negative (as in the great majority of previous cases of inoculation with blood of animals under rabies). But with the saliva it was different. A rabbit inoculated in the ear and abdomen on the 11th of October began to show symptoms of rabies on the 15th, being much excited and damaging the walls of its cage, while it uttered loud cries and slavered at the mouth. Then it fell into collapse and died the following night. The rabbit's body was dissected thirty-six hours after death, and further experiment was made by taking fragments of the right and left submaxillary glands and introducing them under the skin of two other rabbits respectively. These two rapidly succumbed, one on the fifth, the other on the sixth day (becoming visibly ill on the third); neither passed through a furious stage, however, and the predominant feature was paralysis. The important practical result is, that human saliva, such as caused rabies in the rabbit, is necessarily virulent, and would probably have corresponding effects on man; so that it should be dealt with cautiously, and that not only during the life of the person furnishing it, but in post-mortem examinations.

The Agency of Plants in Earth-Building.—The important question of the part taken by plants in earth-building is discussed by Professor Ernst Hallier, of Jena, in a popular essay on "Plants and Man in their Interrelations." The contributions made by the vegetable world to the formation of the crust of the earth are most obviously shown in the beds of peat and coal, the remains of former immense forests and swamps. These formations, remarkable and important as they are. Professor Hallier observes, are far exceeded by the less apparent changes which are effected by the agency of plants. The deposits of freshwater limestones are largely the results of plant-action. Nearly all the streams in calcareous regions bring down carbonate of lime in solution as a bicarbonate. Their waters being charged with carbonic acid or having absorbed it from the air, are by its aid enabled to act upon the otherwise insoluble carbonate of lime, and to take up a quantity of it proportioned to the amount of carbonic acid they contain. This dissolved lime is in its turn converted by the plants which grow in and under the water into stone. All the carbon that is needed for the organic world, animals as well as plants, is obtained through the action of plants in extracting carbonic acid from the air. Plants and those parts of plants which are under water do not stand in direct relations with atmospheric air, but are dependent on the carbonic acid which is held in the water, and, when this is exhausted, on the dissolved bicarbonate of lime. A part of the carbonic acid is taken up from this substance by the chlorophyl-cells, while the other part remains fixed in the lime in the form of simple carbonate of lime. Since the latter is insoluble in water, it is deposited just where it happens to be, which in this case is on the surface of the plant, and this becomes covered with a coating of limestone. Fresh supplies of water bring down new stores of carbonic acid and the dissolved bicarbonate of lime, and the plants continue their work of converting the latter into the insoluble carbonate. Thus the work goes on Unceasingly, and crust on crust of limestone is deposited on millions of small plants. The plants themselves die, wholly incased in stone, but new ones succeed them, and the layers of petrified plants bear in continuous succession a green coating of growing plants. Strata are added to strata, and the limestones grow enormously through the quiet activity of the charæ, mosses, reeds, grasses, and other plants in the water. Fresh-water limestones are thus still in process of formation in all limestone regions. The minor valleys of the Thuringian Valley contain large bodies of soft, fresh-water limestones, in which the forms of the plants to whose action they are due may be plainly recognized, partly in incrustations, partly in impressions, mixed with fresh-water shells and with remains of the trees which once grew on the shore. The material, though soft, has been used in the manufacture of a building-stone out of which cities like Jena and many towns have been built. Rock-building of this kind has been going on ever since there was a growth of plants on the earth, and has during that time played a considerable part in forming the crust of the earth. Other far smaller plants