Oct. lo, 1889] 



NATURE 



579 



may stimulate even the feeblest amongst us to walk in his footsteps 

 if only for a short distance, whose life is a consistent endeavour to 

 seek after truth if haply he may find it, whose watchwords are 

 simplicity, fahhfulness, and industry, and whose sole ambition is 

 to succeed in widening the pathway of knowledge so that follow- 

 ing generations of wayfarers may find their journeys lightened 

 and their dangers lessened. 



Such men are not uncommon amongst the ranks of distinguished 

 chemists. 1 might have chosen as an example the life and labours 

 of your sometime townsman, Joseph Priestley, had not this theme 

 been already treated by. Prof. Huxley, in a manner I cannot 

 approach, on the occasion of the inauguration of the .statue which 

 stands hard by. To-day, however, I will select another name, 

 that of a man still living, the great French chemist — Pasteur. 



As a chemist Pasteur began life, as a chemist he is ending it. 

 For although, as I shall hope to point out, his most important 

 researches have entered upon fields hitherto tilled, with but scanty 

 success, by the biologist, yet in his hands, by the application of 

 chemical methods, they have yielded a most bountiful harvest of 

 new facts of essential service to the well-being and progress of 

 the human race. 



And after all the first and obvious endeavour of every culti- 

 vator of science ought to be to render service of this kind. For 

 although it is foolish and shortsighted to decry the pursuit of any 

 form of scientific study because it maybe as yet far removed from 

 practical application to the wants of man, and although such 

 studies may be of great value as an incentive to intellectual 

 activity, yet the statement is so evident as to almost amount to a 

 truism, that discoveries which give us the power of rescuing a 

 population from starvation, or which tend to diminish the ills 

 that flesh, whether of man or beast, is heir to, must deservedly 

 attract more attention and create a more general interest than 

 others having so far no direct bearing on the welfare of the race. 



" There is no greater charm," says Pasteur himself, "for the 

 investigator than to make new discoveries, but his pleasure is 

 more than doubled when he sees that they find direct application 

 in practical life." To make discoveries capable of such an appli- 

 cation has been the good fortune — by which I mean the just 

 reward — of Pasteur. Ho v he made them is the lesson which I 

 desire this evening to teach. I wish to show that these dis- 

 coveries, culminating as the latest and perhaps the most remark- 

 able of all, in that of a cure for the dreaded and most fearful of 

 all fearful maladies, hydrophobia, have not been, in the words of 

 Priestley, "lucky haphazardings," but the outcome of patient and 

 long-continued investigation. This latest result is, as I shall 

 prove to you, not an isolated case of a happy chance, but simply 

 the last link in a long chain of discoveries, each one of which 

 has followed the other in logical sequence, each one bound to the 

 other by ties which exhibit the life-work of the discoverer as one 

 consequent whole. In order, however, to understand the end 

 we must begin at the beginning, and ask ourselves what was the 

 nature of the training of hand, eye, and brain which enabled 

 Pasteur to wrest from Nature secret processes of disease the dis- 

 covery of which had hitherto baffled all the efforts of biologists. 

 What was the power by virtue of which he succeeded when all 

 others had failed, how was he able to trace the causes and point 

 out remedies for the hitherto unaccountable changes and sick- 

 messes which beer and wine undergo ? What means did he adopt 

 to cure the fatal silkworm disease, the existence of which in the 

 south of France in one year cost that country more than one 

 hundred millions of francs ? Or how did he arrive at a method for 

 exterminating a plague known as fowl cholera, or that of the 

 deadly cattle disease, anthrax, or splenic fever, which has killed 

 millions of cattle, and is the fatal woolsorters' disease in man ? 

 And last but not least how did he gain an insight into the 

 working of that most mysterious of all poisons, the virus of 

 hydrophobia ? 



To do more than point out the spirit which has guided Pasteur 

 in all his work, and to give an idea of the nature of that work 

 in a few examples, I cannot attempt in the time at my disposal. 

 Of the magnitude and far-reaching character of that work we 

 may form a notion, when we remember that it is to Pasteur that 

 we owe the foundation of the science of bacteriology, a science 

 treating of the ways and means of those minute organisms called 

 microbes, upon whose behaviour the very life, not only of the 

 animal, but perhaps also of the vegetable, world depends — a 

 science which bids fair to revolutionize both the theory and prac- 

 tice of medicine, a science which has already, in the hands of Sir 

 Joseph Lister, given rise to a new and beneficent application in 

 the discovery of antisej^lic surgery 



The whole secret of Pasteur's success may be summed up in 

 a few words. It consisted in the application of the exact methods 

 of physical and chemical research to problems which had hitherto 

 been attacked by other less precise and less systematic methods. 

 His early researches were of a purely chemical nature. It is 

 now nearly forty years ago since he published his first investiga- 

 tion. But this pointed out the character of the man, and 

 indicated the lines upon which all his subsequent work was laid. 

 Of all the marvellous and far-reaching discoveries of modem 

 chemistry, perhaps the most interesting and important is that of 

 the existence of compounds which, whilst possessing an identical 

 composition — that is, made up of the same elements in the same 

 proportions — are absolutely different substances judged of by 

 their properties. The first instance made known to us of such 

 isomeric bodies, as they are termed by the chemist, was that 

 pointed out by the great Swedish chemist Berzelius. He showed 

 that the tartaric acid of wine-lees possesses precisely the same 

 comp isition as a rare acid having quite different properties and 

 occasionally found in the tartar deposited from wine grown in 

 certain distric's in the Vosges. Berzelius simply n )ted this 

 singular fact, and did not attempt to explain it. Later on, Biot 

 observed that not only do these two acids differ in their chemical 

 behaviour, but likewise in their physical properties, inasmuch as 

 the one (the common acid) possessed the power of deviating the 

 plane of a polarized ray of light to the right, whereas the rare 

 acid has no such rotatory power. It was reserved, however, for 

 Pasteur lo give the explanation of this singular and at that time 

 unique phenomenon, for he proved that the optically inactive acid 

 is made up of two compounds, each possessing the same com- 

 position, but differing in optical properties. The one turned out 

 to be the ordinary dextro-rotatory tartaric acid ; the other a new 

 acid which rotates the plane of polarization to the left to an 

 equal degree. As indicating the germ of his subsequent re- 

 searches, it is interesting here to note that Pasteur proved that 

 these two acids can be separated from one another by a pro- 

 cess of fermentation, started by a mere trace of a special form of 

 mould. The common acid is thus first decomposed, so that if the 

 process be carried on for a certain time only the rarer laevo- 

 rotatory acid remains. 



Investigations on the connection between crystalline form, 

 chemical composition, and optical properties, occupied Pasteur 

 for the next seven years, and their results — which seem simple 

 enough when viewed from the vantage-ground of accomplished 

 fact — were attainable solely by dint of self-sacrificing labours such 

 as only perhaps those who havethemselves walked in these enticing 

 and yet often bewildering paths can fully appreciate, and by 

 attention to minute detail as well as to broad principles to an 

 extent which none can surpass and few can equal. A knowledge 

 of the action of the mould in the changes it effects on tartaric 

 acid led Pasteur to investigate that bete noire of chemists, the pro- 

 cess of fermentation. The researches thus inaugurated in 1857 

 not only threw a new and vivid litjht on these most complicated 

 of chemical changes, and pointed the way to scientific improve- 

 ments in brewing and wine-making of the greatest possible value, 

 but were the stepping-stones to those higher generalizations which 

 lie at the foundation of the science of bacteriology, carrying in 

 their train the revolutions in modern medicine and surgery to 

 which I have referred. 



The history of the various theories from early times until our 

 own day which have been proposed to account for the fact of the 

 change of sugar into alcohol, or that of alcohol into vinegar, 

 under certain conditions, a fact known to the oldest and even the 

 most uncivilized of races, is one of the most interesting chapters 

 in the whole range of chemical literature, but, however enticing, 

 is one into which I cannot now enter. Suffice it here to say that 

 it was Pasteur who brought light out of darkness by explaining 

 conflicting facts and by overturning false hypotheses. And this was 

 done by careful experiment, and by bringing to bear on the sub- 

 ject an intelligence trained in exact methods and in unerring 

 observation, coupled with the employment of the microscope and 

 the other aids of modern research. 



What now did Pasteur accomplish? In the first place he 

 proved that the changes occurring in each of the various pro- 

 cesses of fermentation are due to the presence and growth of a 

 minute organism called the ferment. Exclude all traces of these 

 ferments, and no change occurs. Brewers' wort thus preserved 

 remains for years unaltered. Milk and other complex liquids do 

 not turn sour even on exposure to pure air, provided these in- 

 finitely small organisms are excluded. But introduce even the 

 smallest trace of these microscopic beings, and the peculiar 



