Composition and control of ileal contents.

The nutrient supply to the colonic bacterial flora probably consists of 60-70 g fermentable substrate; up to 15 g may be protein and the remainder is carbohydrate. In addition, there may be 5 g long-chain fatty acid. The proximal colon is the main site of bacterial metabolism in the colon. However, the key problem is the inaccessibility of the caecum, and the difficulty of studying its ecology. In a stable ileostomy the last few centimetres of ileum take on the appearance of a colonic mucosa, and this model is the best that we have for the caecum. All methods of study are open to criticism, and it is essential that a variety of methods be used and constantly checked against the results of indirect measures.