Oxalates, expressed as anhydrous oxalic acid, have been shown to occur to the extent of about 10% on a dry basis in
spinach, New Zealand spinach, Swiss chard, beet tops, lamb's quarter, poke, purslane and rhubarb. Traces were found in nearly all vegetables and fruits.
If to a diet of meat, peas, carrots and sweet potatoes, relatively low in calcium but permitting good though not maximum growth and bone formation, spinach is added to the extent of about 8% to supply 60% of the calcium, a high percentage of deaths occurs among rats fed between the age of 21 and 90 days. Reproduction is impossible. The bones are extremely low in calcium, tooth structure is disorganized and dentine poorly calcified. Spinach not only supplies no available calcium but renders unavailable considerable of that of the other foods. Considerable of the oxalate appears in the urine, much more in the feces.
Turnip greens, mustard greens, kale and collards, greens with negligible oxalates, under similar conditions produce excellent animals that deposit four times as much calcium per
unit body weight as those receiving spinach.