residual vitality of expressed protoplasm, and not to a rela- 

 tively simple enzyme, as is sometimes supposed ; and in review- 

 ing the position, he states that " the work of Molisch carries 

 with it the greatest conviction, and leads one to conclude that 

 photosynthesis can exist to a small degree apart from the 

 living cell. One may further hazard the hypothesis that this 

 function is correlated with some machinery more complex than 

 an enzyme, but much less complex than a complete protoplas- 

 mic unit." 



The work of Bach * and Polacci has been adversely criti- 

 cized by Euler. f Polacci found that if an extract of active 

 leaves be distilled, the presence of formaldehyde may be de- 

 tected in the distillate. On repeating these experiments, 

 Euler found that the extract gave a feebler reaction when 

 compared with the distillate and, what is of greater importance, 

 ordinary hay gave results as good as those obtained from fresh 

 green leaves. Euler also experimentally examined Bach's re- 

 sults ; it will be remembered that Bach found that carbon di- 

 oxide and water may be made to combine in the presence of 

 sunlight, provided that a sensitizer, not necessarily chlorophyll, 

 be present. Euler found that if carbon dioxide be not used, 

 formaldehyde is still produced, although in smaller quantities ; 

 further, that the passage of nitrogen or hydrogen, in place of 

 the carbon dioxide, through the solution of uranium acetate, 

 yielded as good results ; finally, in the experiments of which 

 dimethylaniline was used, the resulting formaldehyde was due 

 to impurities in the sensitizer employed. 



The question has received renewed attention recently owing 

 to the conclusions arrived at by Usher and Priestly.J Sum- 

 marizing their results, they found that normally the photolysis 

 of carbon dioxide and water leads to the formation of hydrogen 

 peroxide and formaldehyde, although under certain conditions 

 formic acid may be produced. Of these two products, the 

 hydrogen peroxide is decomposed by an enzyme in the plant, 

 and the formaldehyde is condensed by the protoplasm. Thus 

 in the presence of light and chlorophyll carbon dioxide and 



*Bach: "Compt. rend.," 1893, 116, 1145. 

 t Euler : " Ber. deut. chem. Gesells.," 1904, 37, 3411. 



Usher and Priestly : " Proc. Roy. Soc., Lond.," B., 1906, 77, 369 ; 1906, 

 78, 318 ; 1911, 84, 101. 



