Why has it been so hard and why does it continue to be difficult to identify these pluripotent cells within tissues?

为什么会那么难呢,为什么在组织中识别多能干细胞,始终困难重重呢

耶鲁公开课 - 生物医学工程探索课程节选

These cells are rare and so it's been hard to identify them, that's part of it.

这些细胞太少了,所以很难找到,这是原因之一

耶鲁公开课 - 生物医学工程探索课程节选

You'd be hard pressed to identify what the meter of that is so that's one reason, and of course what--where am I going with the next important point about what's happening in this music?

你会很难确定其中的节拍,这也是原因之一,当然这也是我将要讲解的下个关键点,关于在这类音乐中的情形

耶鲁公开课 - 聆听音乐课程节选

One reason it's been harder to identify stem cells is that they're so rare; the other reason is that it's hard to identify the characteristics of them and it's taken many years to work this out.

干细胞难以识别的原因之一是,这些细胞很少,另一个原因就是,干细胞的特征性蛋白难以识别,我们花了好多年去解决这个问题

耶鲁公开课 - 生物医学工程探索课程节选