It has long been known that the level of serum iron in animals falls during infection.
人们早就知道，在感染期间，动物的血清铁水平会下降。
2
One family of completely harmless snakes, the kingsnake, has also evolved serum that neutralizes rattlesnake venom.
一种完全无毒的蛇家族，王蛇，也进化出了能中和响尾蛇毒液的血清。
3
The virus was first identified in the State Serum Institute in Copenhagen, Denmark, in 1958 during an investigation into a pox-like disease among monkeys.