How many?

Micrograms

In the metric system, a microgram or microgramme is a unit of mass equal to one millionth (1×10−6) of a gram.

Slugs

The slug is a derived unit of mass in a weight-based system of measures, most notably within the British Imperial measurement system and the United States customary measures system. A slug is defined as the mass that is accelerated by 1 ft/s2 when a net force of one pound (lbf) is exerted on it.