1. Inclusion of raw kidney bean (Phasealus vulgaris) proteins in the diet for rats was shown to affect the weight of some internal organs. Of these, in addition to the well-known hypertrophy of the pancreas attributable to dietary trypsin inhibitors, the observed atrophy of the thymus and the doubling in weight of the small intestine are related to the protein or lectin content of the bean diet, or both.
2. Changes in tissue composition of the small intestine were also recorded. Its protein content increased by about 40–50% and carbohydrate content doubled suggesting the occurrence of increased mucinous glycoprotein secretion. Increased DNA content (by about 30–40 %) however also indicated mucosal hyperplasia.
3. Changes were also observed in mineral content, urea concentration and some enzyme activities in sera and urine, possibly as a result of disturbances in systemic metabolism or hormone levels, or both.
4. The results gave further support to previous suggestions that the oral toxicity of kidney-bean lectins involves local reactions in the small intestine in combination with their effects on the systemic immune system and general metabolism.