1. After experimental small bowel by-pass the excluded segment of intestine, whether jejunum or ileum, shows a decrease (expressed in units/cm of intestine) in mucosal weight, protein, RNA and activity of all eight enzymes studied (leucyl β-naphthylamidase, alkaline phosphatase, β-galactosidase, α-glucosidase, aryl sulphatase, β-glucuronidase, cytochrome oxidase and catalase). There is a fall in DNA content and there are no consistent changes in enzyme activity when expressed as units/mg of DNA.
2. The intestine remaining in continuity after small bowel by-pass shows an increase (expressed in units/cm of intestine) in mucosal weight, protein, RNA and enzyme activity. There is an accompanying rise in DNA content in the intestine in continuity.
3. The increased values of all variables measured in the intestine in continuity are much more marked in ileum than in jejunum.
4. The adaptive changes seen in the by-passed intestine and the intestine in continuity are a result of ‘hypoplasia’ and ‘hyperplasia’ respectively.