August 24, 191 1] 



NATURE 



265 



studied medicine at Marburg, but subsequently pursued 

 chemistry at Heidelberg under Leopold Gmelin. Having 

 relinquished medicine on taking his degree, he obtained 

 the privilege of working with Berzelius in his laboratory 

 at Stockholm. On his return from Sweden in 1824 he 

 was appointed teacher of chemistry in the Trade School in 

 Berlin. Some years later he became professor in the 

 University of Gottingen. Soon after his return from 

 Sweden he met Liebig in Frankfort, and a close intimacy 

 at once sprang up, which continued for more than forty 

 years to the end of Liebig 's life. Two volumes of their 

 correspondence have been compiled by Hofmann, and the 

 perusal of these letters, extending from 1829 to 1873, 

 affords a view of the subjects which occupied the minds 

 of both, as well as many of the incidents of their lives. 

 One only we have time to notice here. Liebig paid 

 several visits to England, and in a letter to Wohler dated 

 from Giessen, November 23, 1S37, he tells him that he has 

 travelled through England. Ireland, and Scotland in every 

 direction, and has seen many surprising things, but has 

 learned little. The absence of scientific knowledge in 

 England he attributes to the badness of the teaching. In 

 another letter, addressed to Berzelius nearly at the same 

 time (November 26), he says : — " England ist nicht das 

 Land der Wissenschaft," only there is a widespread 

 " dilettantismus," and he complains that "die Chemiker 

 schamen sich Chemiker zu heissen, weil die Apotheker, 

 welche verachtet sind, diesen Namen an sich gezogen 

 haben." 



Liehig's contributions to pure chemistry, though so 

 numerous and important, can be recalled onlv briefly. 

 They may be placed under three heads, namely, first, the 

 invention and perfecting of a method for analysing organic 

 compounds, which in all essential features is still practised 

 everywhere. 



Secondlv, the discovery of a large number of new com- 

 pounds, of which even the names cannot now be mentioned 

 for want of time, but which include chloroform and chloral 

 and many cyanides. He also established the formula of 

 uric acid and the nature of aldehyde. 



Thirdly, we owe to Liebig the conception of the theory of 

 Kmpound radicals, which arose out of his researches jointlv 

 with Wohler (1S32) into the products from essential oil of 

 bitter almonds. 



In a letter to Wohler (May 26. iS-,q), Liebig writes that 

 he is 01 eupied with the study of the phenomena of fermenta- 

 tion rind putrefaction, and having sent an account of his 

 views to Wohler, another letter, dated June 3, discusses the 

 criticism which he has received from him. In the postscript 

 to this long- and interesting letter, we find a concise state- 

 ment of Liebig's hypothesis concerning the action of fer- 

 ments. 



Bi fore proceeding further, it will he well to understand 

 what is meant by fermentation. If we take a solution of 

 sugar, and add to it a very small quantity of brewers' 

 yeast, or, if we take grape juice without any addition, in a 

 short time, especially in warm weather, a frothing, clue to 

 the escape of minute bubbles of gas, soon sets in. and this 

 continue? until the liquid has lost its sweet taste, and has 

 become more or less alcoholic and intoxicating. The escap- 

 ing gas is carbon dioxide, vulgarly called carbonic acid, 

 and the liquid retains, beside alcohol as the chief product, 

 small quantities of other things. Somewhat similar 

 changes go on in the leavening of bread, the souring 

 of milk, the putrefaction of merit, and apparently also in 

 the animal body in the course of many feverish diseases. 

 One peculiarity of the process consists in the fact that the 

 ferment, the veast for example, serves to bring about 

 Ehemical decomposition in a relatively large, almost in- 

 ilel"i"i. ly large, quantity of the sugar or other substance in 

 solution. 



's explanation of these changes was based on 

 purely mechanical ideas as to the motions of the hypo- 

 thetical particles or atoms. He imagined the atoms of a 

 Substance which causes fermentation or putrefaction to be 

 ,in a state of unceasing vibratory motion, and that this 

 state of agitation was communicated to the molecules of the 

 sugar, causing them to undergo an internal rearrangement, 

 and to break down into simpler structures of a more 

 Stable nature, in the case of alcoholic fermentation of sugar, 

 in fact, into alcohol and carbon dioxide. 



Liebig made the mistake of ignoring, as nearly all 

 NO. 2l82, VOL. 87] 



' chemists and biologists of that time ignored, the constitution 

 of the ferment. In 1859 and following years, Pasteur, the 

 great French chemist, demonstrated the essentially vitalistic 

 character of the phenomenon, and showed that the destruc- 

 tion of the sugar was an effect concomitant with the growth 

 and multiplication of the cells of a minute organism, visible 

 under the microscope. A special form and character of 

 organism is concerned in each type of fermentation. 



The organised character of yeast had been proved many 

 years before by the observations of Kutzing, Cagniard 

 Latour, and Schwann. Nevertheless, the views of Liebig 

 prevailed for some time. In the English version of his 

 famous letters on chemistry, in the fourth edition, which 

 appeared in 1859, there is a chapter headed "Theory which 

 ascribes fermentation to fungi refuted." As a matter of 

 fact, it was about this time established. 



Liebig was ultimately convinced of the organic nature 

 of yeast, but he still contended for his theory of molecular 

 destruction by communicated agitation, as furnishing the 

 explanation of the physiological act which comes about 

 within the cells of the yeast. An important step was taken 

 much later, when, in 1897, it was shown by Buchner that 

 something can be dissolved out of yeast which, indepen- 

 dently of the cells, is capable of resolving sugar into 

 alcohol and carbon dioxide. Thereupon, it seemed to some 

 that Liebig's views might be resuscitated. But the changes 

 which occur are now known to be very complicated, in- 

 volving, in the first place, a process, not of destruction, but 

 of building up molecules of a. more complex nature, before 

 they are broken down into the final products of fermenta- 

 tion. Liebig's theory, therefore, disappears from the scene. 



Before 1S40 it may be stated as almost literally true 

 that physiology in the modern sense of the term did not 

 exist, and certainly there was but a small basis for chemical 

 physiology. The chemical production of urea independently 

 of animal life, by Wohler, in 1S28, was a fact of which 

 the deep significance appeared only much later. The studies 

 in organic chemistry, into which Liebig had plunged alone, 

 or in conjunction with his friend, necessarily attracted his 

 attention to problems connected with the phenomena of 

 animal and vegetable life. His visit to England, in T837, 

 was largely occupied with observation of the methods of 

 agriculture then prevalent, and during the succeeding years 

 we find in the catalogue of his scientific papers, many signs 

 of his activity in pursuit of questions connected with the 

 application of chemistry to agriculture, the growth and 

 nutrition of plants, the formation of fat in the animal body, 

 the composition and classification of foods, the source of 

 animal heat, and the chemical processes connected with 

 respiration and digestion. It is not possible for us to enter 

 freely into the discussion of all these great subjects, but 

 we must glance at Liebig's views in regard to two of them, 

 not because those views have retained their predominance, 

 but because of the stimulus they gave to inquiry and the 

 encouragement he gave by precept and example to the 

 fundamental principle on which the greater part of modern 

 science is built, namely, the constant appeal to nature, not 

 only by observation, hut bv systematic experiment. 



In Liebig's time all biological processes were supposed 

 to be controlled bv what was called "vital force," that is, 

 somi tiling which is not mechanical force, nor heat, light, 

 electricity, nor chemical affinity. We are still a long way 

 from knowing what life is, but to show how far some 

 physiologists have travelled in the opposite direction, I will 

 make a" very short quotation from a recent book. Con- 

 cerning the use of the word " metabolism," which is a com- 

 prehensive word covering all chemical changes which go 

 on in the bodv during life, the writer directs attention to 

 its implication "that all the phenomena of life are, at 

 bottom, chemical reactions. When a muscle twitches no 

 less than when a gland secretes, it is not too much to 

 say that when we are moved to tears or laughter, it_ is 

 chemical reactions that are the underlying causes to which 

 ultimate analysis must lead us." I quote this as an extreme 

 view. 



Tat its turn first to Liehig's classification of foodstuffs. 

 It is necessary to account for the maintenance of the 

 animal functions, the growth and repair of the body, the 

 maintenance of its temperature. 



Liebig attributed, as we believe correctly, the heat pro- 

 duced in the bodv to the process of burning, which goes 

 ■ on in the tissues in consequence of the absorption of 



