Clinicopathological Tests of Ageing 95 



problems of the aged and in providing the politicians and 

 administrators with factual information concerning a cross- 

 section of the population. The survey undertaken by van 

 Zonneveld (1955) in Groningen was even more valuable in 

 that a complete physical examination was included. The 

 survey at present being undertaken in Holland under the 

 direction of van Zonneveld is still more comprehensive since 

 it covers the whole country and includes, besides a full medical 

 and social history, a complete physical examination and an 

 assessment of mental function. Such comparative studies of 

 the whole human organism provide valuable information as 

 to the probable proportions of the population at say 60, 70, or 

 80 -f- who are partially sighted, blind, deaf, unable to look 

 after themselves, bedridden etc. The defects named, however, 

 are all readily measurable, but it does not follow that all 

 abnormalities have been detected. Moreover, these studies 

 are horizontal studies and must inevitably include many 

 subjects suffering from disease, albeit unrecognized. What 

 are needed are longitudinal studies in which individuals or a 

 group of individuals are continuously observed over many 

 years, and preferably for their whole life, in order that the role 

 of heredity, environment and disease may be properly as- 

 sessed. Limited longitudinal studies have been undertaken 

 in the case of certain specific diseases, which have added 

 greatly to our knowledge of the natural history of disease. 

 In the matter of ageing it would seem that there are very 

 many inherent difficulties even in a longitudinal study. 

 There is not only difficulty of maintaining constant standards 

 with changing personnel but also the constant pressure to 

 revise methods, the effect of changing environment on the 

 sample, it being impossible to maintain the environmental 

 factors constant and also the effect of increasing knowledge in 

 extending diagnostic accuracy. Some value might be ob- 

 tained from longitudinal studies such as the continuation of 

 the studies initiated by the late Sir James Spence in New- 

 castle (Spence et al, 1954) and more particularly with regard 

 to heredity through a study of homologous twins. 



