200 MUTATIONS 



C=CH 



HX C=0 



NORETHYNODREL 



PROGESTERONE 



ESTRADIOL 



Figure 26. Structures of oral contraceptive agent and related 

 hormones. 



caffeine, and I shall dwell on it at length. The special position of caf- 

 feine rests on three facts: first, that it is certainly a mutagen (1, 19, 25, 

 26, 33, 43, 62) ; second, that people who are exposed to caffeine are 

 exposed continuously, every day of their adult lives; and third, that 

 a very large part of the population of the world is exposed, both in 

 coffee-drinking countries like the United States, and in tea-drinking 

 areas like Great Britain or the Far East. There has been some con- 

 fusion about the caffeine content of tea, which I think should be cleared 

 up. Caffeine is the main alkaloidal constituent of tea. People who 

 drink tea for its mild psychic stimulation obtain that effect from the 

 caffeine it contains. The amount of caffeine in a very strong cup of tea 

 is roughly comparable with that in an ordinary cup of coffee. If people 

 drink very weak tea, as in the Far East, the intake would have to be 

 much larger to get the same effect, but the total amount drunk in those 

 cases probably is much larger. So I think it would be fair to say that 

 coffee and tea are approximately equivalent as sources of caffeine 

 exposure. 



Caffeine is depicted in Figure 27, together with the natural nucleic 



