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LIEBIG 415 he announced the discovery hy Wohler of the composition of urea and the method of making it artificially. The association requested him to draw up two reports, one onisomeric bodies, the other on organic chemistry. The response was made in 1840, in a work dedicated to the British association,' entitled Die organische Chemie in ihrer Anwendung auf Agricultur (Brunswick, 1840), which was translated into English from the manuscript by Dr. Lyon ' Playfair, under the title " Chemistry in its Ap- plication to Agriculture and Physiology." In the preface Liebig states that his object in the work was "to develop, in a manner corre- spondent to the present state of science, the fundamental principles of chemistry in general, and the laws of organic chemistry in particular, in their applications to agriculture and physi- ology; to the causes of fermentation, decay, and putrefaction ; to the vinous and acetic fermentations ; and to nitrification. The con- version of woody fibre into wood and mineral coal, the nature of poisons, contagions, and miasms, and the causes of their action on the living organism, have been elucidated in their chemical relations." This work was soon followed by the Chemische Briefe, which was translated into English under the title " Familiar Letters on Chemistry and its Re- lations to Commerce, Physiology, and Agri- culture." The effect of these letters in Ger- many, as stated by Liebig in his preface to the English edition of 1843, was " to lead to the establishment of new professorships in the universities of Gottingen and Wiirzburg for the express purpose of facilitating the application of chemical truths to the practical arts of life, and of following up the new line of investiga- tion and research, the bearing of chemistry upon physiology, medicine, and agriculture, which maybe said to be only just begun." In June, 1842, Liebig presented to the British as- sociation a second report in response to their request of 1838. This was entitled Die Thier- chemie oder organische Chemie in ihrer Anwen- dung auf Physiologic und Pathologie (Bruns- wick, 1842). It was translated into English from the author's manuscript by Prof. William Gregory and published as " Animal Chemistry, or Chemistry in its Application to Physiology and Pathology." Great practical good resulted from Liebig's investigations, which soon led to a better appreciation of the nature and proper application of medicines and food. This par- ticular subject continued to occupy his atten- tion, and papers frequently appeared in the Annalen and other scientific journals present- ing the results of further investigations. These were embodied in two works, Chemische Un- tersuchvngen uber das Fleisch und seine Zube- reitung zum Nahrungsmittel (Leipsic, 1847), and Die Ursachen der Saftebewegung im thieri- schen Organismus (Brunswick, 1848), translated by Prof. Gregory, "Researches on the Chem- istry of Food," and " The Motions of the Juices in the Animal Body." The nature of the ani- 494 VOL. x. 27 mal tissues and of the liquid compounds of the body was fully investigated in these works, and the passage of their elements from one to another was carefully traced. The practical application is found in the observations upon the cooking of food, and the suggestions by which this process may be conducted with greater economy and more exact knowledge of the objects to be attained in the effect of the ali- ment upon the system. Liebig engaged with others in several publications besides those named. With Poggendorff he compiled the Handworterbuch der Chemie (9 vols., Bruns- wick, 1837-'64), and he contributed to Geiger's Handbuch der Pharmacie (Heidelberg, 1839) the portion devoted to organic chemistry, which afterward appeared as a separate work. He also furnished in 1841 the organic portion of Dr. Turner's " Elements of Chemistry." In 1848 he established, in connection with Prof. Kopp, an annual report on the progress of chemistry, which, with the aid of others as contributors, has been continued to the present time. In 1855 appeared his Qrundsdtze der Agriculture hemie, in 1856 Theorie und Praxis der Landwirthschaft, and in 1859 Naturwis- senschaftliche Briefe uber die moderne Land- wirthschaft, translations of which have been published in several languages. Liebig gave much attention to the subject of the utilization of the sewage of cities ; and his letters setting forth the continual loss in fertilizing material which is experienced in all the great food-pro- ducing countries of the world, and which must be greatly augmented when the supplies of guano are exhausted, were read with no little interest by scientific and thoughtful men. The sewage of cities he regarded as the best source from which to restore this loss. Of late years his name has acquired a wide publicity in con- nection with his extractum car?iis or " essence of meat." One of his favorite subjects was that of fermentation, and his explanation of the phenomena as being due to the action of a substance whose molecules are in a state of transition upon the fermenting body was long and ably maintained, and cannot be said to be yet superseded, although there is a general ten- dency to the adoption of the strictly germ the- ory of Pasteur. His last investigation on the subject was published in 1870, in which he ably upholds his theory against Pasteur's ex- planation, and his views and arguments are as forcibly and clearly expressed as we find them in his early publications. His last communica- tion to the Annalen is a notice of the discov- ery of chloroform, published in March, 1872, in which he calls attention to the fact that it was discovered by himself in 1831, and not by Soubeirain, as is generally supposed in Europe. The influence which Liebig exerted on the progress of discovery^ in chemistry is due to his high powers of generalization united to in- domitable perseverance. As a critic he was unsparing and sometimes bitter, but paid the greatest respect to truth and candor. As an