CHEMISTRY OF VEGETATION.

The phenomena of vegetation, no less than those of the animal world, had, however, during the last fifty years been placed by the chemist on an entirely new basis.

Liebig, in 1860, asserted that the whole of the carbon of vegetation was obtained from the atmospheric carbonic acid, which, though only present in the small relative proportion of four parts in 10,000 of air, was contained in such absolutely large quantity that if all the vegetation on the earth’s surface were burned, the proportion of carbonic acid which would thus be thrown into the air would not be sufficient to double the present amount.  That this conclusion was correct needed experimental proof, but such proof could only be given by long-continued and laborious experiment.

It was to our English agricultural chemists, Lawes and Gilbert, that we owed the complete experimental proof required, and this experiment was long and tedious, for it had taken forty-four years to give a definite reply.

At Rothamsted a plot was set apart for the growth of wheat.  For forty-four successive years that field had grown wheat without the addition of any carbonized manure, so that the only possible source from which the plant could obtain the carbon for its growth was the atmospheric carbonic acid.  The quantity of carbon which on an average was removed in the form of wheat and straw from a plot manured only with mineral matter was 1,000 lb., while on another plot, for which a nitrogenous manure was employed, 1,500 lb. more carbon was annually removed, or 2,500 lb. of carbon were removed by this crop annually without the addition of any carbonaceous manure.  So that Liebig’s prevision had received a complete experimental verification.

CHEMICAL PATHOLOGY.

Touching us as human beings even still more closely than the foregoing was the influence which chemistry had exerted on the science of pathology, and in no direction had greater progress been made than in the study of micro-organisms in relation to health and disease.  In the complicated chemical changes to which we gave the names of fermentation and putrefaction, Pasteur had established the fundamental principle that these processes were inseparately connected with the life of certain low forms of organisms.  Thus was founded the science of bacteriology, which in Lister’s hands had yielded such splendid results in the treatment of surgical cases, and in those of Klebs, Koch, and others, had been the means of detecting the cause of many diseases both in man and animals, the latest and not the least important of which was the remarkable series of successful researches by Pasteur into the nature and mode of cure of that most dreadful of maladies, hydrophobia.  The value of his discovery was greater than could be estimated by its present utility, for it showed that it might be possible to avert other diseases besides hydrophobia by the adoption of a somewhat similar method of investigation and of treatment.