10 Phj'-siologie. 



trifugirten Mehlproben auf Kartonpapier aufzutragen, wonach sich 

 die Unterschiede in Stickstoffgehalt durch stärkere oder schwächere 

 Färbung deutlich abheben. Hugo Fischer (Berlin). 



Meldola, R., The living organism as a chemical agency; 

 a review of some of the problems of photos3mthesis by 

 growing plants. (Trans. Chem. Soc. London. Vol. LXXXIX. 



p. 749—770. 1906.) 



An introduction to this presidential address emphasises the 

 important advances that may be expected when chemist and physio- 

 logist attack the problems of vital chemistry in intelligent Cooperation. 

 A detailed exposition of our present knowledge of the problems of 

 photosynthesis follows. Assuming that formaldehyde intervenes in the 

 chemical sequence, there are two classes of problems: 1^. those 

 concerned with the reduction of carbonic acid and 2". those concerned 

 with the condensation to sugar and proteid. Summing up all the 

 recent work on the first stage it is held that the formation of 

 formaldehyde is almost if not quite conclusively proved. This leads 

 to consideration of the question whether we are dealing with a 

 purel}' chemical photolytic process in this stage, as Usher and 

 Priestley's work indicates or with a change for which the vitality 

 of protoplasm is essential. Then the question of the reduction of 

 aqueous carbonic acid directly to formaldehj^de in the chemical 

 laborator}^ is discussed. There is no trustworthy evidence that this 

 has been carried out in Solution. A silent electric discharge through 

 COo and Ho O vapour may possibly give rise to CO and Ho and 

 those are known to combine to give formaldehyde under these 

 conditions which however are remote from those occurring in 

 Solution in the cell. 



As regards the condensation stage it is permissible to assume 

 that the synthesis of carbohydrates Starts from formaldehyde but the 

 sequence of changes is a matter of hypothesis supported by chemical 

 analogies. Various chemical suggestions can be made but none of 

 the intermediate products has been detected in plants. Whether the 

 condensing agent is protoplasm or an organic katalyst it seems to 

 run to the end so quickly that the intermediate products never 

 accumulate. From formaldehyde to fructose the laboratory evidence 

 is fairly complete but beyond this the plant's resources leave the 

 laboratory quite behind though dextrose maj'- be formed from it by 

 isomerisation in alkaline Solution. Saccharose, probably a fundamental 

 sugar in the plant, eludes all laborator}'' s^mthesis. 



The synthesis of the ultimate proteid constituents — amino- 

 acids — from carbohydrate has not been achieved chemically by 

 any method likely to take place in the cell. Meldola dwells upon 

 the possibility that quaternary Compounds ma3^ well arise in photo- 

 synthesis by Union of the N of ammonia with much simpler ternary 

 bodies than carboh3^drates and rather favours the view of Brunner 

 and Chuard that continuous photolytic reduction of carbonic acid 

 may give rise to the whole series of C, H, O, radiales whence bj'- 

 Union and condensation there maj^ be direct formation of a host of 

 different organic Compounds. 



Perhaps too much attention has been focussed on the main 

 product carboh\'drate, and the reasonableness of "multiple photo- 

 synthesis" of subsidiär}'' products must alwaj^s be borne in mind. 



F. F. ßlackman. 



