266 



NATURE 



[August 24, 191 1 



atmospheric oxygen. Liebig was also right in his assertion 

 that animals do not necessarily derive fat from their food, 

 but the animal body is a laboratory, in which fat may be 

 manufactured from carbohydrates, such as sugar and starch. 

 The substance burned in the body is material derived from 

 the food, but it has long been known that the substance 

 thus burned does not consist exclusively of sugar, starch, 

 and fat, which Liebig called respiratory foods. 



The other constituents of food, now included under the 

 general term protein, which contain nitrogen, and are 

 more or less like white of egg in properties, he called 

 plastic foods. These were supposed to produce new tissue, 

 or repair waste, and to be the source of muscular energy 

 or power to do work. 



It is now known that the case is by no means so simple, 

 and, in fact, this classification now possesses only historical 

 interest. The whole question when considered in the light 

 of modern knowledge is, in fact, a mass of difficulties, and 

 very far from being clear of serious controversy. Liebig 's 

 name is associated in the public mind almost exclusively 

 with the extract of meat, which he prepared for the first 

 time in connection with his studies of food. This is to do 

 him less than justice. Liebig never proposed it for use as 

 a substitute for meat, because it contains only a part of 

 the constituents of flesh. It appears that his idea, in the 

 first instance, was to turn to account the flesh, which 

 would otherwise be wasted, of animals which in Australia 

 and South America were then bred solely for the sake of 

 their wool and fat. Extract of meat is to be regarded as 

 a valuable stimulant to be consumed together with bread 

 or other vegetable food. 



Let us now turn to the investigations into the operations 

 and theories of agriculture with which Liebig's name 

 should be for ever associated. Whence do plants get their 

 carbon and nitrogen, which, together with hydrogen and 

 oxygen and water, form the material of their tissues? 

 What is the use of the mineral substances found in the ash 

 left on burning vegetable matter? Why are different soils 

 adapted to different crops, and what is it that gives fertility 

 to a soil? 



The state of knowledge on such subjects is indicated 

 roughly by the summary which had been provided by the 

 lectures of Sir Humphry Davy in 1813. During the subse- 

 quent twenty-five years very little had been done in the way 

 of experiment, but it would be only fair to mention the 

 name of the great French agricultural chemist Boussingault 

 as one of the pioneers a little in advance of Liebig in the 

 study of such questions. Briefly, the position was some- 

 what as follows : it was known that plants decompose the 

 carbonic acid of the air, using the carbon and letting the 

 oxygen go free, but it was commonly supposed that the 

 brown or black substance in the soil, which is usually 

 called humus, and is the result of the decay of preceding 

 vegetable growth, was the chief source of the carbon in 

 growing vegetables. Liebig pointed out that this was 

 impossible, because it failed to show from what source the 

 original plants from the decay of which humus was formed 

 derived their carbon. Liebig was the first to study care- 

 fully the mineral constituents of plants and to recognise 

 the importance of certain substances, especially potash and 

 phosphates. The services which Liebig rendered to the 

 world in connection with plant physiology and agriculture 

 are, however, less to be recognised in the shape of positive 

 contributions to knowledge than in the example set and in 

 the influence of that example in stimulating systematic 

 investigation of agricultural questions. By 1840 Liebig 

 was one of the most famous chemists in the world, and the 

 effect of his inquiries is shown in the activity which 

 became manifest almost immediately after the communica- 

 tion of his first report to the British Association at the 

 fow meeting in 1840. In Germany the Government 

 instituted a large number of Versuchs Stationer in different 

 parts of the country, and in 1843 the systematic experi- 

 ments were started at Rothamstcd which must for ever 

 plao the names of Lawes and Gilbert among the bene- 

 of the world. 



Mm here I must pause to remind myself and my hi 



thai the subject of my lecture is Liebig and his influence 



on thr- progress of modern chemistry. He died in 1873; 



'■in the period of his greatesl activity in science lies further 



by thirty years. Since either period vasl cl 



NO. 2l82, VOL. 87] 



have been brought about by chemical discovery, which, be 

 it always remembered, is based on experimental work in 

 the laboratory. That is the reflection which supplies the 

 explanation of Liebig's great influence on the progress of 

 science. That influence was fully recognised by the genera- 

 tion of chemists now passing away, or almost gone, and it 

 seems to be a duty to preserve as long as possible a memory 

 so rich in past benefits and so full of suggestion for future 

 use. 



Liebig made many discoveries in chemistry ; but his great 

 and permanent service to the woi Id was not in the isolation 

 and study of individual compounds or series of compounds, 

 nor in the conception of theories of chemical action, nor 

 even in views which he promulgated concerning the opera- 

 tions of agriculture, the composition of food, the processes 

 of digestion, or the source of animal heat. His great 

 service consisted in showing how chemistry should be 

 studied and how it should be taught, in setting the example 

 of submitting all questions to the light obtained by direct 

 experimental study of nature, and in thus affirming and 

 illustrating the principle that what is called pure science 

 is of greater permanent value than what is called applied 

 science ; a knowledge of the laws of nature is more useful 

 than many inventions. 



In the Giessen laboratory were trained a considerable 

 number of chemists, many of whom became the teachers of 

 the next generation. From these teachers and their pupils, 

 guided by the same principles as those of the Giessen 

 school, came discoveries of first-rate importance. If 

 Hofmann, a student of Liebig's, had not been attracted 

 to the study of aniline, an inconsiderable constituent of 

 coal tar, if his pupil, Perkin, had not been led to a further 

 study of its transformations, we should have had to wait 

 a long time for the coal-tar dyes and the industries con- 

 nected therewith. If a host of workers trained in Liebig's 

 laboratory, and others emulating their example, had not 

 cultivated the study of all sorts of carbon compounds, often 

 unimportant in themselves, we should not have seen the 

 numerous applications of chemistry to medicine — the 

 saccharin, aspirin, antipyrin, sulphonal, &c. — nor the 

 artificial perfumes, such as those of violet and lilac, which 

 are now made independently of the original source in the 

 flowers. Without the foundation work I have mentioned 

 we could not now have the beginnings of the true physio- 

 logy based on the study of chemical and physical processes 

 and reactions, nor the possibility of following the changes 

 brought about by all sorts of ferments, on the combined 

 results of which we may hope to have a complete develop- 

 ment of a scientific system of medicine and the treatment 

 of disease. 



But there is one other direction of Liebig's activity to 

 which I have not alluded. Discoveries in the study of nature 

 are of little value unless they can be communicated to that 

 part of the world which can and will make use of them. 

 Up to the end of the eighteenth century there were no 

 means of publication except, on one hand, through the 

 transactions of the half-dozen academies, and these were 

 the only scientific periodicals, or, on the other, by the 

 special treatises prepared by investigators for the pur- 

 pose of making known their own discoveries or opinions. 

 Thus we have the famous works of Robert Boyle on the 

 Spring of the Air, and the Sceptical Chemist, Schei Ii 's 

 works on Air and Fire, Priestley's Experiments and 

 Observations on different kinds of Air, Dalton's New 

 Chemical Philosophy, and many others. The publication of 

 such bonks was often accomplished only after years of pre- 

 paration. In iS;2 Liebig founded the Annalen which have 

 ever since borne his name. Out of Trommsdorff's old 

 Annalen dcr Pharmacie Liebig created a journal which has 

 been for eighty years one of the chief repositories of the 

 besl products of the laboratories of the German Empire. 

 Into this journal were poured the results of Liebig's and 

 Wohler's several or joint researches. At the lime of 

 Liebig's death, in 1873, 165 volumes of the Annalen had 

 appeared, and thi re has been an equal number sine*- that 

 date. 



I need '1" no more than 1 tion the titles of the " Hand- 



worterbuch " which Liebig, with the cooperation of his 

 friends Poggendorff and Wohler, produced between iS^fi 

 and 1856, the " Handbuch der Chemie " in 1843, and the 

 famous "Letters on Chemistry," which were originally 



