MUTAGENS OF POTENTIAL SIGNIFICANCE 203 



numbers seriously, I would want to know precisely how the measure- 

 ments were made. 



Goldstein: These experiments were not done in a chemostat but 

 under controlled conditions, in minimal medium, with the addition of 

 mutagenic compounds at comparable — - 



Novick: Did you measure the mutation with what is called the 

 Benzer mutation index? 



Goldstein: Yes, or what I called P, which is the same thing. I am 

 talking about mutant frequency at the end of exponential growth, 

 where both the treated and the control cultures have reached the same 

 total growth from the same small inoculum, and therefore have been 

 at risk the same number of times. 



Novick: It is difficult to speak of rate without taking into account 

 selective effects. 



Goldstein: I would like to continue my discussion of caffeine now. 

 First, I shall consider the exposure of the population to caffeine. In 

 order to make any estimate of potential mutagenic hazard, we have to 

 know what actual concentrations of caffeine people are exposed to, 

 and, more specifically, to what concentrations and for how long the 

 gonads are exposed. 



I mentioned before that the amount of caffeine contained in what we 

 might call an average cup of coffee is between 130 and 150 mg. This, 

 obviously, depends on the strength of the coffee and the person's in- 

 dividual taste. A strong cup of tea contains about the same. Cola 

 drinks contain only a small amount of caffeine compared with coffee 

 and tea. 



There are two ways to get at the mean caffeine levels. One is by 

 doing what Dr. Magni suggested before; that is, taking the total 

 consumption derived from the sales of coffee, tea, and cola drinks, 

 dividing by the total population to obtain a mean daily intake, and 

 then, using our knowledge of the absorption and blood levels estab- 

 lished from a given intake, calculate the mean concentration in the 

 body. 



The other way is to get evidence on the average number of cups of 

 coffee or tea that people drink and then make the same kind of calcula- 

 tion. Both these lead to approximately the same result. In Table 

 4 are figures on the average coffee, tea, and cocoa consumption in this 

 country for several periods. I don't have data for the war years them- 

 selves, but it is well known that the consumption of coffee goes up 

 during periods of national stress. The major consumption of caffeine 

 in the United States is in the form of coffee, as you can see, but 



