INTRODUCTION

The first successful tissue culture was reported 100 years ago when the medullary plate from a chick embryo was successfully maintained in warm saline for 4 to 5 days (Roux, 1885). However, it was not until the introduction of methods based initially on lymph (Harrison, 1907) and later plasma clots (Carrel & Burrows, 1910) that cell culture, as opposed to cell maintenance, became established as a reproducible technique. The link between in vitro culture and lifespan studies was forged at an early stage following the claim that tissue grown in the laboratory was potentially immortal (Carrel, 1912, 1914; Ebeling, 1922). This belief persisted until it was demonstrated that human fibroblast cultures had a finite, reproducible lifespan (Hayflick & Moorhead, 1961; Hayflick, 1965), a finding which primarily was responsible for the rapid adoption of cell culture methods in the study of ageing. Evidence that the lifespan of diploid fibroblasts in vitro was governed by the number of their cell divisions rather than absolute time in culture (Dell'Orco et al, 1973; Goldstein & Singal, 1974; Harley & Goldstein, 1978) served to further emphasize the potential of cell cultures in this field of research.

A number of authors have disputed the validity of fibroblast models in the study of ageing on theoretical and practical grounds. For example, it has been proposed that the loss of division potential exhibited by ageing fibroblasts represents differentiation into a non-cycling stage rather than senescence per se (Bell et al, 1978).