CARBOHYDRATES. 55 



beginning of all the asymmetry in the organic world is centered in the 

 assimilation of the carbon dioxide, for evidently it is here in the plant 

 cell that the first asymmetric synthesis is carried out which continues 

 constantly in the production of only asymmetric compounds. 1 It is 

 indeed possible that chlorophyll, which is itself asymmetrically consti- 

 tuted, plays an important part in this asymmetric synthesis. The first 

 appearance of asymmetry is, however, unexplained. Its existence evi- 

 dently coincides with the formation of the first cell. It is possible, on 

 the other hand, that the plant cell produces first of all an inactive com- 

 pound, for example, an inactive sugar, and that asymmetry first develops 

 by the cleavage of this compound. 2 The animal organism receives in turn 

 with its food, this asymmetry of its body-substance from the plant 

 world, partly directly, as in the case of the herbivora, and partly 

 indirectly, as in the case of the carnivora. We shall find, moreover, 

 that these relations are so suited to the animal organism that it some- 

 times directly disintegrates racemic compounds, and in many cases utilizes 

 only one component and discards the other unchanged. 



The first observed assimilation product of the carbon dioxide and water 

 was starch, easily recognized by means of the iodine reaction. For a long 

 time it was held to be the primary product of assimilation. Gradually it 

 became a recognized fact that starch is a product formed secondarily from 

 more simple components, and little by little the opinion gained ground 

 that d-glucose was to be regarded as the primary product of assimilation. 

 This assumption was supported by the discovery that leaves which have 

 been preserved in the dark are capable of forming starch directly if solu- 

 tions containing hexoses are placed upon them. In general, the following 

 compounds are assimilated: d-glucose, d-mannose, d-galactose, and 

 d-fructose. Other similar compounds may be utilized; thus, mannitol 



1 Cf. Emil Fischer: "Die Chemie der Kohlehydrate und ihre Bedeutung fur die 

 Physiologic." 



2 Cf. A. Byk: Z. physiol. Chem. 49, 641 (1904). Byk seeks to trace the formation 

 of asymmetry back to circularly-polarized light which maybe produced by the reflection 

 of plane-polarized daylight by the surface of the sea. The revolution of the plane of 

 polarization by the magnetism of the earth makes it impossible for equal amounts of 

 the two forms of light to exist at any point on the earth, or upon the whole surface 

 of the earth, or for any considerable period. It is indeed possible that such may be 

 the explanation of the asymmetry of the first cells, but it is scarcely probable that it 

 accounts for the continuous production of asymmetric molecules, for it is unreasonable 

 to assume that one and the same kind of light is permanently in excess at one and the 

 same point on the earth's surface; and it would seem likely, furthermore, that compo- 

 nents of unlike optical products would be formed in different localities. Again, Byk's 

 proof that by means of circularly-polarized light racemic compounds can be split off is 

 not perfectly satisfactory. Furthermore, chlorophyll itself has optical properties. It 

 undoubtedly changes the sun's rays of short wave lengths, which have no effect upon 

 the assimilation, into active, longer wave lengths. 



