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. Author manuscript; available in PMC: 2015 May 13.
Published in final edited form as: Interdiscip Top Gerontol. 2014 May 13;39:45–61. doi: 10.1159/000358899

Fig. 2.

Fig. 2

Diagrammatic representation of the history of cell strains and the phenomenon of cell alteration. Phase I.: the primary culture terminates with the formation of the first confluent sheet. Phase II. is characterized by luxuriant growth necessitating many sub-cultivations. Cells in this phase are termed “cell strains”. An alteration may occur at any time, giving rise to a “cell line” whose potential life is infinite. Conversely, cell strains characteristically enter Phase III. and are lost after a finite period of time. (reproduced with permission from ref [3])