34 The Nature of Biological Diversity 



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In the first experiment of this type in 1950, in which we used the 

 cyclotron as a source of ionizing radiation, 30 we started with COi«, 

 hydrogen, and water, and were ahle to get, by random transformation 

 processes, reduced carbon compounds such as formic acid, acetic acid, 

 and succinic aid. In later experiments, in which ammonia was added 

 to the initial mixture following Miller, 32 glycine was obtained. Still 

 more recently (in the last three or four months) we have performed 

 this experiment again, but instead of depending upon ordinary ana- 

 lytical methods to find these randomly occurring compounds, we have 

 used carbon-14 labeled methane in the primitive gas mixture, thus 

 providing radioactive carbon atoms which could be followed around. 

 The discharge from a 5-Mev electron linear accelerator was passed 

 through the mixture of methane, ammonia, and water, and we took 

 the water solution containing the product from this bombardment 

 and spread it out on a piece of filter paper in a systematic way. 33 



Figure 9 shows the results of one of these bombardment experi- 

 ments. It is a photograph of the darkened x-ray film which results 

 when a paper chromatogram containing radioactive products is placed 

 on top of an x-ray film. Wherever there is a black spot on the film a 

 particular compound has been located. We can tell what the nature 

 of the compound is by where it is located on the film with respect to 

 its origin. All the different nonvolatile radioactive compounds which 

 result from one particular bombardment are shown in Fig. 9, and 

 about a dozen compounds have separated out. 



We have been able to identify in this way some half dozen com- 

 pounds,* including adenine, glycine, alanine, and various other amino 

 acids and sugars, some fatty acids and some hydroxy acids — the very 

 things of which today's living matter is composed. One of the com- 

 pounds, representing about 60 per cent of the total, is urea. We find in 

 neutral and acidic fractions a large number of compounds, including 

 lactic acid and sugars. You can also see that alanine and glycine 

 represent a very small amount of the total. Down in the lower center 

 of the chromatogram are the nucleosides and further up are the bases. 

 There are present in this irradiated mixture adenine, cytosine, 

 guanine, thymine, and perhaps other as yet undetermined bases. 

 Thus, such random processes as these may give rise to all the simple 

 compounds that are needed by present-day living organisms. 3435 



Having made these simple compounds (particularly the amino 

 acids) by the random methods, we can build them up into proteins 



* HCN was identified in the aqueous solution by a separate procedure. 



