Capital Is Part of the Coronavirus Cure

U.S. stocks capped their worst week since 2008 Friday amid fears that the coronavirus will become a pandemic. Though markets rallied Monday on expectations that central banks will slash interest rates, the Nasdaq was still down nearly 9% from its record close of 9817.18 on Feb. 19.

Nasdaq Inc. saw record messages and volumes last week. Nasdaq options markets registered an all-time peak of 62 billion messages on Friday, far above its daily average of about 18 billion over the past year. Similarly, Nasdaq U.S. equities volumes this week reached...