112 HISTORY OF THE OCEANS 



definitive organism, it is first necessary to find in what way it is 

 possible to combine in one small unit all the essentials for metabo- 

 lism. This was not necessary before, because all the essentials 

 would have been found somewhere or other over a large area and 

 sooner or later — they must have taken years to do so — got to 

 where they were wanted. Now the major essential for metabolism, 

 without which the enzymes and the coenzymes could not function, 

 is a source of energy, and this energy can be provided either 

 immediately by light or it can be drawn from substances in which 

 energy has been stored by the previous action of light. These 

 alternatives form the fundamental distinction between the vege- 

 tative and the animal way of living, of which the vegetative is 

 clearly the most primitive. 



It happens that these iron and other metal coordination com- 

 pounds that I have mentioned are suitable not only for carrying 

 out enzyme actions but also can absorb light and, being colored, 

 can absorb it where it is very much stronger in the visible region 

 of the solar spectrum. We call it, of course, the visible region, 

 because we have built up chemical receptors that react to the 

 predominant frequencies emitted by the sun. The appearance of 

 photosynthesis is, in my opinion, the key to the development of 

 the organic life as we know it. How complicated a structure need 

 be to have the requirements of photosynthesis and enzymic 

 transformation in one, we cannot say, but it must be relatively 

 small on the vital scale though large on the molecular scale. 

 Kamen (private communication) has found in some of the red 

 bacteria, which are probably very primitive organisms, molecules 

 as small as a virus, that is, about 200 A across, which contain 

 nucleotides, enzymes, and photosynthetic plastids capable of 

 building up sugars from carbon dioxide and water, in other words, 

 all the necessary works of an organism. 



Whether such small bodies can ever have existed independently 

 is another question. However, we do find them in present-day life 

 usually as separate components in the so-called organelles or small 

 bodies that exist inside cells, such as the chloroplasts responsible 

 for photosynthesis, the mitochondria that carry out the enzymic 

 changes which constitute the metabolism, the microsomes that 



