上世纪50年代,康奈尔大学(Cornell University)的克莱夫·M·麦凯(Clive M. McCay)和同事曾将幼龄鼠的血液输入老龄鼠体内,借此检验这一观念。为了做到这一点,他们将两只大鼠的侧腹皮肤缝在一起,使它们连接起来。经过被称作异种共生的这一步后,血管生长出来,两只老鼠的循环系统融合在了一起。幼龄鼠的血液流入了老龄鼠的体内,老龄鼠的血也流进了幼鼠。
Later, Dr. McCay and his colleagues performed necropsies and found that the cartilage of the old rats looked more youthful than it would have otherwise. But the scientists could not say how the transformations happened. There was not enough known at the time about how the body rejuvenates itself.
后来,麦凯博士和同事解剖了老鼠的尸体,发现老龄鼠的软骨看起来比它未经实验的应有状态更年轻。但这些科学家无法说明这种变化是如何发生的。当时,人们对身体恢复活力的方式还没有足够的认识。
It later became clear that stem cells are essential for keeping tissues vital. When tissues are damaged, stem cells move in and produce new cells to replace the dying ones. As people get older, their stem cells gradually falter.
后来,人们清楚地认识到,干细胞对保持组织的活力至关重要。组织受损时,干细胞会进入,生成新细胞来取代失去活力的老细胞。随着年龄的增长,人的干细胞会逐渐衰退。
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