422 



NATURE 



[Sept. I, 1887 



principles upon which all organic syntheses have been effected. 

 We have already seen that as soon as the chemical structure of 

 a body has been ascertained its artificial preparation may be 

 certainly anticipated, so that the firbt step to be taken is the 

 study of the structure of the naturally occurring substance which 

 it is desired to prepare ariiiicially by resolving it into simpler 

 constituents, the constitution of which is already tnown. In 

 this way, for example, Hofmann discovered that the alkaloid 

 coniine, the poisonous principle of hemlock, may be decom- 

 posed into a simpler substance well known to chemists under 

 the name of pyridine. This fact having been established by 

 Hofmann, and the grouping of the atoms approximately deter- 

 mined, it was then necessary to reverse the process, and, starting 

 with pyridine^ to build up a compound of the required constitu- 

 tion and properties, a result recently achieved by Ladenburg in 

 a series of brilliant researches. 'I'he well-known synthesis of 

 the colouring matter of madder by Graebe and Liebermann, 

 preceded by the important r;searches of Schunck, and that of 

 indigo by Baeyer, are other striking examples in which this 

 method has been successfully followed. 



Not only has this intimate acquaintance with the changes 

 which occur within the molecules of organic compounds been 

 utilized, as we have seen, in the syntliesis of naturally occurring 

 substances, but it has also led to the discovery of many new 

 ones. Of these perhaps the most remarkable instance is the 

 production of an artificial sweetening agent termed saccharin, 

 250 times sweeter than sugar, prepared by a complicated series 

 of reactions from coal-tar. Nor must we imagine that these 

 discoveries are of scientific interest only, for they have given 

 rise to the industry of the coal-tar colours, the value of which 

 is measured by millions sterling annually, an industry which 

 Englishmen may be proud to remember was founded by our 

 countryman Perkin. 



Another interesting application of synthetic chemistry to the 

 needs of every-day life is the discovery of a series of valuable 

 febrifuges, amongst which I may mention antipyrin as the most 

 useful. An important aspect in connexion with the study of 

 these bodies is the physiological value which has been found to 

 attach to the introduction of certain organic radicals, so that an 

 indication is given of the possibility of preparing a compound 

 which will possess certain desired physiological properties, or 

 even to foretell the kind of action which such bodies may exert 

 on the animal economy. 



But it is not only the physiological properties of chemical 

 compounds which stand in intimate relation with their constitu- 

 tion, for we find that this is the case with all their phy-ical 

 properties. It is true that at the beginning of our period any 

 such relation was almost unsuspected, whilst at the present time 

 the number of instances in which this connexion has been 

 ascertained is almost infinite. Amongst these perhaps the most 

 striking is the relationship which has been pointed out between 

 the optical properties and chemical composition. This was in 

 the first place recognized by Pasleur in his classical researches 

 on racemic and tartaric acids in 1848 ; but the first to indicate 

 a quantitative relationship and a connexion between chemical 

 structure and optical properties was Gladstone in 1863. Great 

 instrumental precision has been brought to bear en this question, 

 and consequently most important practical applications have 

 resulted. I need only refer to the well-known accurate methods 

 now in every-day u.-e fur the determination of sugar by the 

 polariscope, equally valuable to the physician and to the 

 manufacturer. 



But now the question may well be put, is any limit set to this 

 synthetic power of the chemist ? Although the danger of dog- 

 matizing as to the progress of science has already been shown in 

 too many instances, yet one cannot help feeling that the barrier 

 which exists between the organized and unorganized worlds is 

 one which the chemist at present sees no chance of breaking 

 down. 



It is true that there are those who profess to foresee that the 

 day will arrive when the chemist, by a succession of constructive 

 efforts, may pass beyond albumen, and gather the elements of 

 lifeless matter into a living structure. Whatever may be said 

 regarding this from other standpoints, the chemist can only say 

 that at present no such problem lies within his province. Proto- 

 plasm, with which the simplest manifestations of life are 

 associated, is not a compound, but a structure built up of com- 

 pounds. The chemist may succes- fully synthetize any of its 

 component molecules, but he has no more reason to look forward 

 to the synthetic production of the structure than to imagine that 



the synthesis of gallic acid leads to the artificial production of 

 gall-nuts. 



Although there is thus no prospect of our effecting a synthesis 

 of organized material, yet the progress made in our knowledge 

 of the chemistry of life during the hst fifty years has been very 

 great, and so much' so indeed that the sciences of physiological 

 and of pathological chemistry maybe said to have entirely aiisen 

 within this period. 



In the introductory portion of this address I have already 

 referred to the relations supposed to exist fifty years ago be- 

 tween vital phenomena and those of the inorganic world. 

 Let me now briefly trace a few of the more important steps 

 which have marked the progress of this branch of science 

 during this period. Certainly no portion of our science is of 

 greater interest, nor, I may add, of greater complexity, than that 

 which, bearing on the vital functions both of plants and of 

 animals, endeavours to unravel the tangled skein of the chemistry 

 of life, and to explain the principles according to which our 

 bodies live, and move, and have their being. If, therefore, in 

 the less complicated problems with which other portions of our 

 science have to deal, we find ourselves, as we have seen, often 

 far from possessing satisfactory solutions, we cannot be surprised 

 to learn that with regard to the chemistry of the living body — 

 whether vegetable or animal — in health or disease we are still 

 farther from a complete knowledge of phenomena, even those of 

 fundamental importance. 



It is of interest here to recall the fact that nearly fifty years 

 ago Liebig presented to the Chemical Section of this Association 

 a communication in which, for the first time, an attempt was 

 made to explain the phenomena of life on chemical and physical 

 lines, for in this paper he admits the applicability of the great 

 principle of the conservation of energy to the functions of 

 animals, pointing out that the animal cannot generate more heat 

 than is produced by the combustion of the carbon and hydrogen 

 of his food. 



"The source of animal heat," says Liebig, "has previously 

 been ascribed to nervous action or to the contraction of the 

 muscles, or even to the mechanical motions of the body, as if 

 these motions could exist without an expenditure of force [equal 

 to that] consu;ned in producing them." Again he compares the 

 living body to a laboratory furnace in which a complicated series 

 of changes occur in the fuel, but in which the end-products are 

 carbonic acid and water, the amount of heat evolved being 

 dependent, not upon the intermediate, but upon the final 

 products. Liebig asked himself the question, Does every kind 

 of food go to the production of heat ; or can we distinguish, on 

 the one hand, between the kind of food which goes to create 

 warmth, and, on the other, that by the oxidation of which the 

 motions and mechanical energy of the body are kept up ? He 

 thought that he was able to do this, and he divided food into 

 two categories. The starchy or carbohydrate food is that, said 

 he, which by its combustion provides the warmth necessary for 

 the existence and life of the body. The albuminous or nitro- 

 genous constituents of our food, the flesh meat, the gluten, the 

 casein out of which our muscles are built up, are not available 

 for the purposes of creating warmth, but it is by the waste of 

 those muscles that the mechanical energy, the activity, the 

 motions of the animal are supplied. We see, said Liebig, 

 that the Esquimaux feeds on fat and tallow, and this burning in 

 his body keeps out the cold. The Gaucho, riding on the pampas, 

 lives entirely on dried meat, and the rowing man and pugilist, 

 trained on beefsteaks and porter, require little food to keep up 

 the temperature of their bodies, but much to enable them to 

 meet the demand fur fresh muscular tissue, and for this purpose 

 they need to live on a strongly nitrogenous diet. 



Thus far Liebig. Now let us turn to the present state of our 

 knowledge. The question of the source of muscular power is 

 one of the greatest interest, for, as Frankland observes, it is the 

 corner-stone of the physiological edifice and the key to the 

 nutrition of animals. 



Let us examine by the light of modern science the truth of 

 Liebig's view — even now not uncommonly held — as to the 

 functions of the two kinds of food, and as to the cause of 

 muscular exercise being the oxidation of the muscular tissue. 

 Soon after tha promulgation of these views, J. R. Mayer, whose 

 name as the first expositor of the idea of the conserva:ion of 

 energy is so well known, warmly attacked them, throwing out 

 the hypothesis that all muscular action is due to the combustion 

 of food, and not to the destruction of muscle, proving his case 

 by showing that if the muscles of ihs heart be destroyed in doing 



