The purpose of this study is to better understand whether and to what extent the activity of immune cells in blood varies over time under normal conditions as assessed in healthy subjects. Results of this study will provide the foundation for helping us evaluate changes in immune cell activities in response to surgery and drugs used in anesthesia. The overall purpose of our research is to understand immune health in the context of anesthesia and surgery.

Inclusion Criteria:

1. Age 18-50
2. Good general health

Exclusion Criteria:

1. Recent cold or flu
2. Chronic use of medications affecting the immune system
3. Chronic illness
4. Smoking habit
5. History of drug abuse
6. Current recreational drug use

Study population consists of a community sample.