Sept. I, 1887] 



NA TURE 



423 



■mechanical work the heart would be burnt up in eiglU days ! 

 What does modern research say to this question ? Can it be 

 brought to tlie crucial test of experiment ? It can ; but how ? 

 Well, in the first place we can ascertain the work done by a man 

 ■or any other animal ; we can measure this work in terms of our 

 mechanical standard, in kilogramme-metres or foot-pounds. We 

 <an next determine what is the destruction of nitrogenous 

 tissue at rest and under exercise by the amount of nitrogenous 

 material thrown off by the body. And here we must remember 

 that these tissues are never completely burnt, so that free nitrogen 

 is never eliminated. If now we know the heat-value of the 

 burnt muscle, it is ea y to convert this into its mechanical 

 equivalent, and thus measure the energy generated. What is 

 the result ? Is the weight of muscle destroyed by ascending the 

 Faulhorn or by working on the treadmill sufficient to produce on 

 combustion heat enough when transformed into mechanical 

 exercise to lift the body up to the summit of the Faulhorn or to 

 <lo the work on the treadmill ? Careful experiment has shown 

 that this is so far from being the case that the actual energy 

 developed is twice as great as that which could possibly be pro- 

 duced by the oxidation of the nitrogenous constituents eliminated 

 from the body during twenty- four hours. That is to say, taking 

 the amount of nitrogenous substance cast ofT from the body, not 

 only whilst the work was being done but during twenty-four 

 hours, the mechanical effect capable of being produced by the 

 muscular tissue from \\hich this cast-off material is derived would 

 only raise the body half-way up the Faulhorn, or enable the 

 pi'ixoner to work half his time on the treadmill. 



Hence it is clear that Liebig's proposition is not true. The 

 nitrogenous constituents of the food do doubtless go to repair 

 the waste of muscle, which, like every other portion of the 

 body, needs renewal, whilst the function of the non-nitrogenous 

 food is not only to supply the animal heat, but also to furnish, 

 by its oxidation, the muscular energy of the body. 



We thus come to the conclusion that it is the potential energy 

 of the food which furnishes the actual energy of the body, 

 ■expressed in terms either of heat or of mechanical work. 



But there is one other factor which comes into play in this 

 •question of mechanical energy, and must be taken into 

 account ; and this factor we are as yet unable to estimate in our 

 usual terms. It concerns the action of the mind upon the body, 

 and, although incapable of exact expression, exerts none the less 

 •an important influence on the physics and chemistry of the body, 

 so that a connexion undoubtedly exists between intellectual 

 activity or mental work and bodily nutrition. In proof that there 

 is a marked difference between voluntary and involuntary work, 

 •we need only compare the mechanical action of the heart, which 

 never causes fatigue, with that of the voluntary muscles, which 

 become fatigued by continued exertion. So, tno, we know well 

 that an amount of drill which is fatiguing to the recruit is not 

 felt by the old soldier, who goes through the evolutions auto- 

 matically. What is the expenditure of mechanical energy which 

 accompanies mental effort, is a question which science is 

 probably far removed fiom answering. But that the body 

 experiences exhaustion as the result of mental activity is a well- 

 recognized fact. Indeed, whilst the second law of thermo- 

 dynamics teaches that in none of the mechanical contrivances for 

 the conversion of heat into actual energy can such a conversion 

 be complete, it is perhaps possible, as Helmholtz has suggested, 

 that such a complete conver-ion may take place in the subtle 

 mechanism of the animal organism. 



The phenomena of vegetation, no less than those of the 

 animal world, have, however, during the last fifty years been 

 placed by the chemist on an entirely new basis. Although before 

 the publication of Liebig's celebrated report on chemistry and 

 its application to agriculture, presented to the British Association 

 in 1840, much had been done, many fundamental facts had been 

 established, still Liebig's report marks an era in the progress of 

 this branch of our science. He not only gathered up in a 

 masterly fashion the results of previous workers, but put forward 

 his own original views with a boldness and f^requently with a 

 sagacity which gave a vast stimulus and interest to the questions 

 at issue. As a proof of this I may remind you of the attack 

 which he made on, and the complete victory which he gained 

 over, the humus theory. Although .Sanssure and o'.hers had 

 already done much to destroy the basis of this theory, yet the 

 fact remained that vegetable physiologists up to 1840 continued 

 to hold to the opinion that humus, or decayed vegetable matter, 

 was the only source of the carbon of vegetation. Liebig, giving 

 due consideration to the labours of Saussure, came to the con- 



clusion that it was absolutely impossible that the carbon 

 deposited as vegetable tissue over a given area, as for instance 

 over an area of forest lan-I, could be derived from humus, 

 which is itself the result of the decay of veget.able matter. He 

 asserted that the whole of the carbon of vegetation is obtaine;! 

 from the atmospheric carbonic acid, which, though only present 

 in the small relative pro])ortion of 4 parts in lo,ooo of air, is 

 contained in such absolutely large quantity that if all the vegeta- 

 tion on the earth's surface were burnt, 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 of Liebig's is correct needed experimental 

 proof, but such proof could only be given by long-continued and 

 laborious experiment, and this serves to show that chemical 

 research is not now confined to laboratory experiments lasting 

 perhaps a few minutes, b.it that it has invaded the domain of 

 agriculture as well as of physiology, and reckons the periods of her 

 observations in the field not by minutes, but by years. It is to our 

 English agricultural chemists Lawes and Gilbert that we owe the 

 complete experimental proof required. And it is true that this 

 experiment was a long and tedious one, for it has taken forty- 

 four years to give the definite reply. At Rothamsted a plot was 

 set apart for the growth of wheat. For forty-four successive 

 years that field has grown wheat without addition of any 

 carbonized manure ; so that the only possible source from which 

 the plant could obtain the carbon for its growth is the atmo- 

 spheric carbonic acid. Now, 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 looo pounds, whilst on 

 another plot, for which a nitrogenous manure was employed, 

 1500 pounds more carbon was annually removed ; or 2500 

 pounds of carbon are removed by this crop annually without 

 the addition of any carbonaceous manure. So that Liebig's 

 prevision has received a complete experimental verification. 



May I without wearying you with experimental details refer 

 for a moment to Liebig's views as to the assimilation of nitrogen by 

 plants — a much more complicated an 1 difficult question than the 

 one we have just considered — and compare these with the most 

 modern results of agricultural chemistry? We find that in this 

 case his views have not been substantiated. He imagined that 

 the whole of the nitrogen required by the plant was derived from 

 atmospheric ammonia ; whereas Lawes and Gilbert have shown 

 by experiments of a similar nature to those just described, and 

 extending over a nearly equal length of time, that this source is 

 wholly insufficient to account for the nitrogen removed in the 

 crop, and have come to the conclusion that the nitrogen must 

 have been obtained either from a store of nitrogenous material 

 in the soil or by absorption of free nitrogen from the air. These 

 two apparently contradictory alternatives may perhaps be recon- 

 ciled by the recent observations of Warington and of Berthelot, 

 which have thrown light upon the changes which the so-called 

 nitrogenous capital of the soil undergoes, as well as upon its 

 chemical nature, for the latter has shown that under certain con- 

 ditions the soil has the power of absorbing the nitrogen of the 

 air, forming compounds which can subsequently be assimilated 

 by the plant. 



Touching us as human beings even still more closely than the 

 foregoing, is the influence which chemistry has exerted on the 

 science of pathology, and in no direction has 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 give the names of fermentation and putrefaction, the 

 views of Liebig, according to which these phenomena are of a 

 purely chemical character, have given way under the searching in- 

 vestigations of Pasteur, who established the fundamental principle 

 that these processes are inseparably connected with the life of 

 certain low forms of organisms. Thus was founded the science 

 of bacteriology, which in Lister's h.ands has yielded such splendid 

 results in the treatment of surgical cases ; and in those of Klebs, 

 Koch, William Roberts, and others, has been the means of de- 

 tecting the cause of many diseases both in man and animals ; the 

 latest and not the least important of which is the remarkable series 

 of successful researches by Pasteur into the nature and mode of 

 cure of that most dreadful of maladies, hydrophobia. And here 

 I may be al owed to refer with satisfaction to the results of the 

 i labours on this subject of a Committee the formation of which I 

 I had the honour of moving for in the House of Commons. These 

 ] results confirm in every respect P.i^teur's assertions, and prove 

 j beyond a doubt that the adoption of his metho 1 has prevented 

 the occurrence of hydrophobia in a large proportion of persons 



