546 



SCIENCE: 



[N. S. Vol. XII. No. 302. 



touched. The alkaloid and the fermenta- 

 tion methods are of the widest applicability, 

 and the latter is especially important be- 

 cause of its bearing on vital phenomena. 

 Pasteur showed that the micro-organism is 

 able to attack one of the geometrically iso- 

 meric forms, while incapable of acting on 

 the other. In his work on the sugars 

 Fischer further demonstrated that this se- 

 lective power is not to be ascribed to any 

 peculiar vital property of the living cell, 

 for the soluble ferments, the enzymes, have 

 frequently the same selective power. This 

 power he attributes to the existence of the 

 proper molecular asymmetry in the enzyme, 

 by virtue of which its molecule is able to 

 come into proper relationship with the 

 asymmetric molecule of the body to be 

 fermented ; with exactly the same consti- 

 tution on the part of one of the reacting 

 bodies, but with the opposite configura- 

 tion, this relationship cannot be brought 

 about and fermentation does not ensue ; as 

 Fischer expresses it, sugar and enzyme must 

 be adapted to each other as lock and key. 

 Lock and key may be made on the proper 

 model, but only when the notches of the 

 key are on the same side as the wards of 

 the lock can they fit each other. From 

 this it would follow that the form which is 

 left unattacked during the fermentation 

 with a particular enzyme should be decom- 

 posed by an enzyme having the same chem- 

 ical formula but the opposite configuration. 

 In fact, the phj'siological significance of 

 stereochemistry is so great that we do not 

 yet begin to appreciate it. The carbo- 

 hydrates all contain asymmetric carbon 

 atoms, and the same is unquestionably true 

 of the proteids, all of which are optically 

 active ; the enzymes, as bodies closely re- 

 lated to the proteids, probably possess 

 ■ molecular asymmetry. The different digest- 

 ibility or assimilability of various carbo-hy- 

 drates and proteids may be partly due to the 

 different space configuration of their mole- 



cules rather than to any specifically chem- 

 ical cause. Fischer has suggested the pos- 

 sibility of synthesizing a sugar capable of 

 assimilation by diabetics. The power of 

 digesting cellulose and horny matter pos- 

 sessed by some animals may be due simply 

 to the peculiar configuration of their di- 

 gestive enzymes. The curious fact that 

 dextro-asparagine is sweet, while Isevo- 

 asparagine is insipid, is doubtless due to the 

 asymmetric structure of the active mole- 

 cules of the taste buds. It is possible that 

 a dextro-strychnine might be innocuous, a 

 dextro-quinine a virulent poison. 



It is well known that all asymmetric 

 compounds produced by purely artificial 

 methods consist of an optically inactive 

 mixture of dextro- and Isevo-rotatory forms 

 in equal proportions ; only nature is able 

 to produce one form to the exclusion of 

 the other ; the chemist can do this only 

 with the aid of a natural product such 

 as an alkaloid or enzyme, itself active 

 in one sense, or by intelligent selection, 

 as where Pasteur separated the two tar- 

 trates. At present we can perceive no 

 escape from the dilemma that in the syn- 

 thesis of its optically active substances 

 the organism either employs some ultra- 

 chemical process, or produces them by 

 chemical means through the agency of pre- 

 viously existing active substances. The 

 latter alternation would lead us back to 

 the existence of one-sided asj'mmetry in 

 the very first organism of the series, the 

 origin of which it is equally impossible to 

 explain on chemical grounds. This inter- 

 esting fact, pointed out by Japp * is 

 regarded by him as indicating that some- 

 thiug besides chemical and physical forces 

 was concerned in the original production 

 of life. The difi&culty is a real one, and 

 we still know of no better explanation than 



* Address before Section ' B, ' British Association 

 for the Advancement of Science. Nature, Vol. 58, 

 p. 452. 



