68 PROCESSES OUTSIDE THE LIVING CELL CHAP. 4 



the air in light. Whenever red, brown or blue cells have been found 

 capable of photosynthesis, it could always be proved that they, too, 

 contain the green pigment, even though its color may be masked by 

 carotenoids or anthocyanins. 



It was natural therefore that attempts to repeat photosynthesis 

 outside the plant have centered on chlorophyll preparations. The re- 

 sults have been disappointing, and we need only devote a few lines to 

 these experiments. 



Nobody has ever claimed to have achieved photosynthesis by illuminating a 

 chlorophyll solution in an organic solvent in the presence of carbon dioxide; but a few- 

 negative experiments on this subject have been pubUshed by von Euler (1909). Usher 

 and Priestley (19062) have asserted that chlorophyll films on gelatin produce hydrogen 

 peroxide and formaldehyde when exposed to light and carbon dioxide. But this claim, 

 although supported by Schryver (1910), was discredited by Ewart (1908), von Euler 

 (1909), Schiller and Baur (1912), Warner (1914) and Wager (1914), who proved that, 

 although some formaldehyde can be found after the illumination of chlorophyll films in 

 air, it originates in the oxidation of chlorophyll and not in the reduction of carbon 

 dioxide. Willstatter and Stoll (1918) asserted that no formaldehyde is produced at all, 

 if pure chlorophyll preparations are used. Chodat and Schweizer (1915) claimed the 

 formation of formaldehyde and hydrogen peroxide by the illumination of chlorophyll 

 precipitated on calcium carbonate; but Willstatter and Stoll (1918) failed to confirm 

 this claim. It was thought by Willstatter and Stoll that chlorophyll is contained in 

 the leaves in the colloidal state; they therefore carried out some experiments on the 

 photosynthetic activity of colloidal chlorophyll solutions in water, with completely 

 negative results. They also tried the addition of peroxidase (on the assumption that 

 the completion of photosynthesis requires the decomposition of a peroxide), but without 

 success. Knoll, Matthews and Crist (1938) have described an oxygen evolution caused 

 by the addition of catalase to illuminated aqueous solutions of sodium chlorophyllide 

 and carbonate, but details of this experiment have never been pubUshed. 



We shall find in chapter 14 proofs of the existence in the plant cells 

 of a chlorophyll-protein complex. The preservation of this complex 

 may be necessary to maintain the photosynthetic capacity of chlorophyll. 

 Different methods to extract the chlorophyll-protein complex from leaves 

 have been perfected, and these extracts have been found to possess 

 some of the properties of the chlorophyll in the leaf, e. g., its absorption 

 spectrum, chemical stability and fluorescence. Nevertheless, they, too, 

 lack photosynthetic capacity (c/. Smith 1938). Eisler and Portheim 

 (1923) claimed that artificial chlorophyll protein complexes (prepared by 

 adding horse serum to chlorophyll solutions) were able to reduce carbon 

 dioxide and liberate oxygen in light, but their methods were crude, and 

 the promised detailed publication has not materialized. 



The incapacity of chlorophyll-protein complexes to bring about 

 photosynthesis appears natural if we remember that even isolated 

 chloroplasts maintain, at the utmost, only a vestige of their normal 

 photosynthetic activity. The question to ask about chlorophyll prepara- 



