 Subjects will be considered ambulatory if they are not institutionalized, bedridden, or homebound. Medically stable subjects may have underlying illnesses such as hypertension, diabetes, ischemic heart disease, or hypothyroidism, but their symptomssigns must be controlled with medical therapy. Subjects with acute febrile illnesses oral temperature equal to or exceeding 99.5oF 37.5oC will be deferred until 3 days after illness resolution. 