Age and Membrane Diffusion Coefficients 75 



seventy-eight years. Only the diffusion coefficients of carbon 

 dioxide and glucose were estimated. 



The mean diffusion coefficient values for the age group one 

 to thirty-nine, forty to fifty-nine, and sixty to seventy-eight 

 years are shown in Table IV. In contrast to the findings in 

 the experiments on the aortic samples the data fail to show 

 any consistent change in permeability of the cerebellar 

 tentorium with age. 



Table IV 



Mean Diffusion Coefflclenta ( x 10^) Observed for Various Age Groups for 



Human Tentorium CerebelH, 



Age Group Number of Carbon dioxide Glucose 

 ( Years } samples 



Summary 



Diffusion experiments were carried out with nitrogen, 

 oxygen, carbon dioxide, lactate, iodide and glucose on prepar- 

 ations of the intima and the media of the human thoracic 

 aorta, using the diffusion procedure of Kirk and Johnsen 

 (1951). The diffusion coefficient values showed a definite 

 tendency to increase with the age of the individuals, indicating 

 an increase in tissue permeability with age. 



In contrast to the findings irr the experiments on aortic 

 tissue, diffusion studies on preparations of the human ten- 

 torium cerebelli failed to show any increase in permeability 

 of that tissue with age. 



The investigation was supported by a research grant (PHS-891) from 

 the National Heart Institute of the National Institutes of Health, 

 Public Health Service. 



