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MUTATIONS 



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rIO 



Figure 28A. Blood levels in man after caffeine administration. 

 Caffeine added to decaffeinated coffee and taken by 10 subjects. 

 Curve is drawn through mean values; range shown by vertical 

 lines. 



may summarize all this by saying that caffeine is very rapidly and 

 essentially completely absorbed from the gastrointestinal tract, and is 

 evenly distributed throughout the water phase of all tissues. This 

 necessarily means that caffeine freely enters most (if not all) body 

 cells. 



Figure 28B depicts an experiment of Axelrod and Reichenthal, in 

 which two cups of coffee at a time (caffeine content not measured) 

 were repeatedly administered to human subjects, to find out about 

 cumulation and persistence of caffeine in the body. You see that the 

 subjects drank 8 cups of coffee between 8 a.m. and 6 p.m. As we 

 would expect from the slow decline of the plasma level in Figure 28A, 

 we see that repeated doses raise the plasma level higher and higher, 

 because the rate of administration exceeds the rate of elimination. The 

 level rises to about 4 mg/1 and then falls slowly when no more caffeine 

 is given. It can be calculated from the falling slopes in both experi- 

 ments that the biological half life is about 3.5 hours. After a day of 

 moderate coffee-drinking, the level would fall overnight to a very low 

 point, and without further intake would fall practically to zero the 

 next day. 



It is known, chiefly from the studies of Cornish and Christman (16), 



