THE LIFE-WORK OF A CHEMIST. 493 



life, not ouly of the animal, but perhaps also of the vegetable world de- 

 l)ends, — a science which bids fair to revolutionize both the theory and 

 l)ractice 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 antiseptic 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 physi- 

 cal and chemical research, to j^roblems which had hitherto been at- 

 tacked b}' other less precise and less systematic methods. His early 

 researches were of a i)urely chemical nature. It is now nearly forty 

 years ago since he published his first investigation. But this pointed 

 out the character of the man and indicated the lines upon which all 

 iiis subsequent work was laid. 



Of all the marvellous and far-reaching discoveries of modern chem- 

 istry perhaps the most interesting and important is that of the exist- 

 ence of compounds which while possessing an identical (composition 

 (that is, made up of the same elements in the same proportions), are 

 absolutely <lifterent 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, Ber- 

 zelius. He showed that the tartaric acid of wiue-lees possesses precisely 

 the same composition as a rare acid having quite difi'erent properties and 

 occasionally found in the tartar deposited from wine grown in certain 

 districts in the Vosges. Berzelius simply noted this singular fact, but 

 did not attempt to explain it. Later on, Biot observed that not only 

 do these two acids differ in their chemical behavior, but likewise in 

 their physical properties, inasmuch as the one (the common acid) pos- 

 sessed the power of deviating the plane of a polarized ray of light to 

 the right, wliereas the rare acid has no such rotatory power. It was 

 reserved however for Pasteur to give the explanation of this singular 

 and at that time unique phenomenon, for he proved that the optically 

 inactive acid is made u}> of two compounds, each possessing the same 

 composition 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 researches, it is interesting 

 here to note that Pasteur proved that these two acids can be sepa- 

 rated from one another by a process of fermentation, started by a mere 

 trace of a special form of mold. The common acid is thus first de- 

 composed, so that if the process be carried on for a certain time only 

 the rarer hevo-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 siMii)le enough when viewed from 

 the vantage giouiui of accomplished fact — were attainable solely by 

 dint of self-sacrificing labors such as only perhaps those who have 



