D,— ZOOLOGY. 85 



belongs rather to botany and chemistry than to zoology, I may perhaps 

 for the sake of completeness be allowed to refer to it very briefly. I 

 have already said that. Baly brouglit about the synthesis of formahk-liydc 

 from CO, and H^O under the intluence of rays of very short wave-length 

 (X = 200|i.a) from a mercury-vapour lamp. He was also able to show 

 that when certain coloured substances were added to the solution of 

 carbon dioxide in water the same reaction took place under the influence 

 of ordinary visible light. His explanation of this process is that the 

 coloured substance known as the photocatalyst absorbs the light rays 

 and then itself radiates, at a lower infra-red frequency corresponding 

 to its own molecular frequency, the energy it has absorbed. At this 

 lower frequency the energy thus radiated is able to activate the carbonic 

 acid, so that the reaction leading to the formation of formaldehyde can 

 and does take place. In the living plant this synthesised formaldehyde 

 probably at once polymerises to form sugars. 



Malachite green and methyl orange, as well as other organic com- 

 pounds, were found to act as photocatalysts capable of synthesising for- 

 maldehyde, and Moore and Webster's work had previously shown that 

 inorganic substances, such as colloidal ui'anium oxide and colloidal ferric 

 oxide, can do the same. Chlorophyll in living plants may with some 

 confidence be assumed to operate in a similar way, though no doubt the 

 series of events is more complex, since the green pigment itself is not 

 a single pigment, and others, such as carotin and xanthophyll, are also 

 concerned. 



We have tried to picture the gradual building up from elements 

 occurring in sea-water of a chlorophyll-bearing flagellate, capable of 

 manufacturing its own nourishment and able to multiply indefinitely 

 by the simple process of dividing in two. If we assume only one divi- 

 sion during each night as a result of the day's work in accumulating 

 food material, such an organism would be able in a comparatively short 

 space of time to occupy all the natural waters of the world. But 

 here we are met by a difficulty which is not easily overcome. Chloro- 

 phyll, the photocatalyst, the most essential factor in the building up 

 of the new organic matter, is itself a laighly complex organic substance, 

 and in any satisfactory theory its original formation and its constant 

 increase in quantity must be accounted for. Lankester * has maintained 

 that chlorophyll must have originated at a somewhat late stage in the 

 development of organic life, and has suggested that earlier organisms 

 may have noiurished themselves like animals on oi'ganic matter already 

 existing in a non-living state. An alternative hypothesis, which in 

 view of the recent work seems more attractive, is to suppose that the 

 earlier organisms were either activated by some simpler photocatalyst, 

 or that they received the necessary energy at suitable frequency directly 

 from some outside source. 



It must not be forgotten, also, that at the time these developments 

 were taking place the conditions of the environment would in many 

 ways have been different from those now existing in the sea. One 



' Treatise on Zoologi/, Part I, Introduction. London, 1909. 



