82 ACTION OF LIGHT RAYS 



condition. The organism is enabled by a linked reaction to utilise 

 for building up from carbon dioxide and water those reduced organic 

 substances which form its body material. Similarly, the philo- 

 thionic organisms are capable of utilising the energy of sulphur, or 

 reduced sulphur compounds, to build up organic carbon compounds, 

 and the nitrogen- assimilating organisms fed with organic carbon 

 compounds can link up to the endothermic reactions necessary to 

 convert the atmospheric nitrogen into ammonium salts or nitrites, 

 and from these build up proteins. 



In all cases where the energy of light is absent, however, there 

 must evidently have been previously a light-transforming reaction 

 at some earlier period of history, for without this the metal or lower 

 oxides, or sulphur or sulphide, would never have been formed upon 

 which the organism not utilising light depends for its store of energy. 

 In a world cooling down from red-heat, in presence of free oxygen in 

 its atmosphere, all these substances would have been completely 

 oxidised, and so the immense world deposits of pyrites and ferrous 

 oxide and suchlike reduced substances, just like coal, shale, and 

 petrol, must have originated from previous life processes, accom- 

 panied by energy transformations in presence of sunlight. 



It is accordingly of some interest to enquire whether such trans- 

 formations of sunlight into chemical energy by inorganic trans- 

 formers are associated with a temporary chemical change from a 

 higher to a lower oxide, or whether the change is a surface action in 

 which the light energy is converted into chemical energy at the 

 surface of the colloidal aggregate. 



Our experiments favour the latter view, for if the lower oxide 

 reacted with the water and carbon dioxide to form formaldehyde, 

 then a greater reactivity might be expected when ferrous salts were 

 employed instead of ferric salts; this is, however, not the case, for 

 we have found ferrous salts to be entirely inert, nor have we been 

 able by titration with permanganate to show any formation of 

 ferrous salts when ferric salts are exposed in aqueous solutions in 

 presence of carbonic acid. Moreover, many of the active inorganic 

 transformers which we have lately investigated, as recorded below, 

 do not form higher and lower oxides under the conditions in which 

 we have used them. It is therefore probable that the energy 

 transformation is one induced by the energy of the light at the 

 surface of the colloidal particle upon which probably carbon 

 dioxide concentrates. 



