INTRODUCTION. 



number is sixteen. These are in pairs, twelve of the sixteen are known, and three occur 

 in nature. The relative configurations may be expressed by the following formulae: 



The relative arrangements of the component units of molecules are determined by 

 an arJjitrary standard, because there is no known way of ascertaining the absolute con- 

 figuration. If, therefore, we adopt in any pair a standard formula for the dextro form, 

 the formula of the Isevo form will, of course, be the mirror-image of that of the first ; and 

 the standards for the several pairs will, in their relations to one another, be established 

 ui;)on the same basis. In adtlition to this differentiation in accordance with the qualita- 

 tive effects upon polarized Ught, the various dextro and Ijbvo forms differ in their quanti- 

 tative effects; and, moreover, each form may exist in more than one form. Inasmuch as 

 each asymmetric group has a rotatory value of its own, tlextro or lajvo, it seems obvious 

 that when a compound contains a number of such groups the rotatory power must corre- 

 spondingly be influenced. This conception led van't Hoff to the assumption that when 

 a compound contains a number of asymmetric groups the rotatory power is the algebraic 

 sum of the rotational values of the several groups. Both Guye and Walden have con- 

 firmed, but Rosanoff has disputed, this assumption; but the whole subject of the causes 

 of the quantitative differences in optical activity is under discussion. 



For many years it was believed that the asymmetric carbon atom is specific to living 

 matter, just as was held in respect to organic substances until Wohler in 1S2S synthetized 

 urea. He in common with Darwin, van't Hoff, and almost every discoverer or expositor 

 of some great and revolutionary truth or doctrine was subjected to intemperate criticism, 

 and so insistent were his critics that when all attempts failed to locate the mysterious 

 vital entity in vitro, the proposition that the necessary living factor lay in the presence or 

 manipulations of the chemist certainly carried destructive criticism to its ultra-micro- 

 scopic limit. Since Wohler's time, hundreds and thousands of organic substances have 

 been synthetized in vitro; and it has likewise been found that the asymmetric carbon atom 

 is an atom not merely of life, but of nature. In fact, so impressed were chemists with 

 the specificity of the carbon atom in respect to living matter that its very presence was 

 regarded as sufficient of itself to determine whether or not a given substance was of vital 

 origin. This is well-illustrated in the instances of petroleum, bitumen, and asphaltum, 

 whose origin had been a matter of speculation for generations; but which, since llagusin 

 has shown that petroleum is optically active, has been considered settled. 



