Explain why Henrietta lacks is described as immortal

Hurry 20 mins all the animals were now present except moses, the tame raven, who slept on a perch behind the back door. when major saw that they had all made themselves comfortable and were waiting attentively he cleared his throat and began: "comrades, you have heard already about the strange dream that i had last night. but i will come to the dream later. i have something else to say first. i do not think, comrades, that i shall be with you for many months longer, and before i die i feel it my duty to pass on to you such wisdom as i have acquired. i have had a long life, i have had much time for thought as i lay alone in my stall, and i think i may say that i understand the nature of life on this earth as well as any animal now living. it is about this that i wish to speak to you." which historical figure does old major most likely represent? tsar nicholas ii an imperial guard vladimir lenin joseph stalin