Studies of Human Organ System Function 79 



There is, however, much of additional value to be gained by 

 observation of the unique. Dr. Dickinson Richards has a 

 recent paper on the ageing lung which includes the considera- 

 tion of a few highly selected subjects with no taint of disease. 

 Such few unique individuals deserve most careful study. 



I believe the most useful information is obtained not by any 

 single one of the sampling methods, but with all of them, 

 singly and together. One may successfully weigh and find 

 inconsequential the influence of a small percentage of contami- 

 nation with diagnosed or undiagnosed disorders. One may 

 even deal with a sizeable percentage if agewise bias can be 

 excluded or accounted for. Wherever disease is dominant, 

 any known limitation of the clinical art ought to be fairly 

 recognized, for clinical authority has been defined as "the 

 obsessed state" and the specificity of clinical diagnosis may 

 have a wide range of variation. My approach does not mean 

 at all to deprecate clinical evaluation, or to devalue studies on 

 older humans because there may be a high incidence of patho- 

 logy in clinical or putative normals. Such studies and 

 evaluations are needed, but needed too is cognizance of the 

 limitations of the material. It may be pointed out that this 

 problem in subject selection applies as well to age studies in 

 other species than man ; but the science, as well as the art, of 

 clinical diagnosis has reached higher levels in the human. 



Many of the studies which may be performed in humans do 

 not yield information with a highly specific meaning and, thus, 

 the interpretations of experiments which reveal age differences 

 may be difficult. As examples, the age changes in vitamin B 12 

 excretion after intramuscular injection (Watkin et a/., 1953) or 

 in uric acid excretion after ACTH (Solomon and Shock, 1950) 

 may be the consequence of renal functional change rather than 

 of vitamin deficiency or adrenal functional decline. Although 

 an electrocardiogram appears to be a specific cardiac record 

 because it registers electrical potentials of cardiac origin, this is 

 not quite the case; and particularly, it is not a specific indi- 

 cator of myocardial function. These observations are never- 

 theless valuable, and valid conclusions may be reached 



