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EXAMPLES OF REACTIONS TO STANDARD 

 STIMULI AT DIFFERENT AGES 



K. J. Franklin 



Department of Physiology, Nuffield Research Unit, 

 St. Bartholomew'' s Hospital Medical College, London 



Special research on ageing began in this Department only 

 fifteen months ago and it has been limited to mammals bred 

 (with extremely few exceptions) in the Department, and to 

 Man. The starting point was the idea that reactions to 

 definite stimuli at different ages could be measured, and the 

 changes in reaction with the passage of time could be de- 

 termined. Results could thereafter be analysed, and when 

 sufficient researches had been made, one might begin to get a 

 better appreciation of the meaning and tendency of ageing. 

 This directive was not to be the sole one, but it has proved to 

 be the major one, in the Unit's work to date. 



The first study, by Carter (1956), was of the response of the 

 gingival epithelium of the Merion rat, Meriones libycus, to 

 brushing; it was intended as a precursor to the studies on 

 human subjects which are mentioned below. The brushes 

 used for the rats were specially made. Male subjects in three 

 age groups were tested, the gum on one side of the upper jaw 

 being brushed for one minute, twice daily, for four weeks, 

 while the other side served as a control. The brushing led to a 

 significant increase in the thickness of the cornified layer, and 

 the height of the epithelial papillae was also increased (Figs. 1 

 and 2). Within the range studied, however, which was from 

 early adult to middle age, ageing per se was without significant 

 influence upon the thickness of the cornified layer or upon 

 that of the epithelium. A supplementary study of animals 

 between birth and early adult age has therefore been begun, 

 but results are not yet available. 



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