It was not to be expected that a work like this should at once be adopted without opposition, or a thorough canvas of the conclusions at which the author had arrived. From the very extent and nature of the subject, the author was obliged to accept and adopt the con clusions of physiologists who had not been so accurate in their inves tigations as himself. In subsequent editions of this work ho has however availed himself of all the information brought to bear on his snbject by his critics, and has shown most conclusively that the only prospect for the advancement of agriculture as an art is through a thorough study of the physiology of plants. The effects of this work soon became apparent, more especially in this country, in the regard that was paid to chemical principles in the application of manures. That many errors were committed, that Liebig himself turned out to be wrong in some of his conclusions, was only what could be expected. The application of chemistry to agriculture has however steadily advanced, numerous treatises devoted to this subject have appeared, and certain great advantages have been obtaiued. As an instance of the latter, the extensive application of phosphate of lime in the form of bones, coprolites, and other compounds, when treated by sulphuric acid, may be quoted.
One of the most recent of Liebig's contributions to agricultural chemistry is his work entitled 'Principles of Agricultural Chemistry, with Special References to the late Researches made in England.' This work was translated by Professor Gregory of Edinburgh, and published in London in 1855. It was written in answer to the con clusions arrived at from a long course of experiments by Mr. J. B. Lawea of Berkhampstead. These conclusions were in direct contra diction to the principles previously laid down by the author, and he states, "In fact all the experiments of Mr. Lewes prove exactly the reverse of that which, in his opinion, they ought to demonstrate." Of this work the translator says, "It is, so far as I can judge, by far the best of the author's writings on the important subject to which it refers." This work contains, in the shape of fifty propositions, a summary of the true relation between chemistry and agriculture, and may be regarded as the most matured of the author's works on this important department of chemical inquiry. This controversy appears to have ben conducted on both aides with the most perfect temper and good feeling.
Such works alone as the above might well have made a lasting and enviable reputation ; but from 1840 to 1855 Liebig was eugaged in the production of many other works. In 1837 ho commenced with Wohler a 'Dictionary of Chemistry,' which was published in parts. In 1839 Geiger's 'Handbook of Pharmaceutical Chemistry' was pub lished, in which the part devoted to Orgauic Chemistry was written by Liebig : this part afterwards appeared as a separate work. In 1841
be edited the organic part of the late Dr. Turner's Elements of Chemistry.' The volume on Agricultural Chemistry was regarded by the Author as only an instalment of what he owed the British Association in answer to their request for a report on the progress of Organic Chemistry. At the meeting held at Manchester in June 1842, Dr. Lyon Playfair read an abstract of Professor Liebig's report on Organic Chemistry applied to Physiology and Pathology.' This able production was published in the ' Transactions' of the association. The entire report appeared in 1842, under the title of 'Animal Chemistry, or Chemistry in its application to Physiology and Pathology,' 8vo, London. This work was translated from the author's manuscript by Professor Gregory of Edinburgh; a third and greatly improved edition was published in 1840. This work carried his chemical researches from the vegetable to the animal kingdom. What had been done for the plant, vegetable physiology, and the agriculturist in the first work, was now attempted to be done for the animal, animal physiology, and the medical practitioner. In this work ho pursued the same plan as in the firot : he set aside the hypothesis of a vital principle as a cause in living phenomena, and examined them from a physical and chemical point of view. A strict comparison is instituted between that which is taken into the body in the form of air and food with that which passes out of the body, and all possible knowledge of the laws of organic chemistry is brought to bear upon the intermediate pheno mena of life. In this way he threw a flood of light on processes that had hitherto been wrapped in obscurity. The phenomenon of animal heat was seen to be snore clearly the result of the oxidation of carbon. Certain kinds of food, as starch, sugar, and oil, were pointed out as the sources of the carbon, whilst Mulder's group of proteinaceous compounds were as clearly traced to their destiny in the production of the living tissues. The source of fat iu the aufinal body, in spite.
of the opposition of the French school, was traced to the oxidation of the hydrogen in the starch and sugar of the food. The nature of the excretions, especially of the urine, bile, and faeces, were carefully examined, and manifold new analyses and results were given. The impression this work has made on the science of physiology and the Practice of medicine is not less than that of the last on botany and agriculture. It at once called into activity an amount of chemical investigation that has already led to the most important results, and given a new aspect to all physiological inquiry in the animal kingdom.