Abstract
After a brief historical review of the chemistry of citric acid, the author summarized the citric acid content of human serum, blood, milk, urine, semen, cerebro-spinal fluid, amniotic fluid, sweat, tears, aqueous and vitreous humors, muscle, liver, kidney, brain, thyroid gland, bone,skin, hair, in some instances giving parallel data from other animals than man. The author then discusses exogenous citric acid, endogenous citric acid, the identity of citric acid as distinguished from isocitric acid, and the biological significance of citric acid.