Crystals of plant and animal products do not typically occur naturally. In 1840 F. L. Hünefeld published his accidental observation of the first protein crystals— those of hemoglobin—in a sample of dried menstrual blood pressed between glass plates.
Hünefeld, Der Chemismus in der thierischen Organisation, Leipzig: Brockhaus, 1840, 158-63.
Lesk, Protein Structure, 36. Tanford & Reynolds, Nature’s Robots, 22. Judson, Eighth Day of Creation, 489.