1909.] Formation of Formaldehyde ifi Green Plants. 231 



mixture with water, extraction with etker, etc., in the method given above 

 (see p. 228) for the modified formaldehyde test. In this case, carbon dioxide 

 or formaldehyde was probably formed by the photochemical decomposition 

 of other substances in the crude chlorophyll, for Neuberg has recently 

 shown that a large number of organic substances readily undergo decom- 

 position on exposure to light in the presence of optical sensitisers, such as 

 uranium salts.* When carbon dioxide was present, the formaldehyde reaction 

 was visible when the ordinary test was applied, without having to dilute 

 with water and extract the chromatogenic base with ether. In no case, 

 however, was the formation of formaldehyde demonstrable when the films 

 were kept in the dark. These experiments were carried out several times 

 with different chlorophyll preparations, and yielded always the same results. 

 Only very small quantities of chlorophyll need be employed in each 

 experiment. In the quantities employed for each of the experiments 

 described a])ove, no formaldehyde could be detected in the original film 

 by any of tlie given methods of testing. 



Mechanism of the Reaction. 

 It has been generally objected to the conception of the formation of 

 formaldehyde as an intermediate product of sugar synthesis in plants, that 

 this substance is highly toxic. This objection has, however, lost some of its 

 weight as a result of the experiments of Tr^boux,t who states that certain 

 plants, when placed in very dilute solutions of formaldehyde, can synthesise 

 therefrom starch. 



The fact that formaldehyde after synthesis by chlorophyll exists in the 

 state of fairly stable combination with some product «r group, explains how 

 the quantity of the aldehyde present can be automatically regulated. The 

 action of formaldehyde on various organic substances, especially those 

 containing the amino-group, has been studied by Schiff.J 



He has shown that in many cases the reaction between an amino-group 

 and the aldehyde is a reversible one, as in the case of the amino-acids — 

 E E 

 CH.NH2+ HCHO ^ CH.N : CH2 + H2O. 

 COOH COOH 



In some cases this reaction proceeds to completion only in the presence 

 of a large excess of the aldehyde.§ In other cases, as in that of 

 * ' Biochem. Zeitsch.,' 1908, vol. 13, p. 305. 

 t ' Flora,' 1903, p. 73. 



X ' Liebig's Annalen,' 1899, vol. 310, p. 2.5 ; 1901, vol. 319, pp. 58 and 287 ; and 1902, 

 vol. 325, p. 348. 



§ Compare Sorensen, 'Biochem. Zeitscli.,' 1008, vol. 7, p. 45. 



vor,. Lxxxir. — b. t 



