Because there is no limit and there is less prescription there certainly today than in the disease model.

因为没有界线，如今它的使用程度,也远比疾病模型少。

哈佛公开课 - 幸福课课程节选

And they did that by intentionally infecting calves, by harvesting their skin when they were at a certain point of the disease, and by isolating the virus from the skin of the calves.

他们有意感染很多小牛,当小牛疾病发展到一定程度,就收割牛皮,然后把病毒从牛皮里分离出来

耶鲁公开课 - 生物医学工程探索课程节选