{'fraction_non_alphanumeric': 0.022584228063680118, 'fraction_numerical': 0.014068863383931877, 'mean_word_length': 4.536885245901639, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
The length and mucosal surface area of the small and large gut in young rats.

A knowledge of the dimensions of the gut mucosa is useful in studies on intestinal absorption. Although values for length and surface area of the whole or parts of the absorptive gut in adult rats have been reported by Verzar & McDougall (1936), Wood (1944), Fisher & Parsons (1950) and Boyne, Fell & Robb (1966), there appear to be no satisfactory figures reported for young growing rats, which are often used in absorption and nutrition experiments. We therefore offer here a summary of some measurements on the small and large gut of a group of young rats and a comparison of their mucosal areas per unit gut length in different regions with those of adult rats previously reported in the literature (Table 1). The body weights and gut lengths were measured in 25 randomly selected male Sprague-Dawley rats aged 5 weeks. After killing the rats by a blow on the head the guts were dissected free without tension and pinned out flat. Measurements were made of the duodenum (from the pylorus to the distal attachment of the pancreas), the combined jejunum and ileum, the caecum, and the colon (to the pelvic brim). The mucosal area determinations were made in 4 rats by the method of Fisher & Parsons (1950) which involves making measurements on tracings of magnified longitudinal and transverse sections cut from Bouin fixed, paraffin embedded segments of gut. In the calculations a correction was made for shrinkage due to fixation and embedding. The gut segments we used were taken from six sites, named and located as follows: Duodenum, 3-5 cm from the pylorus; Jejunum, 10 cm from the pylorus; Midgut, midway between the pylorus and the ileocaecal junction; Ileum, 3 cm above the ileocaecal junction; Upper colon and lower colon, 4 cm and 8 cm respectively below the ileocaecal junction. The mucosal area per unit gut length ratio in these young rats shows a distally falling gradient of about 2: 1 over the length of the small gut. The effects on surface area of varying degrees of folding of the mucosa and the presence of villi are seen more clearly in the values for relative area per unit length of the different parts of the small gut compared with the colon as unity, i.e. considering the colon as a tube of the same diameter as the small gut with flat mucosa. Comparing the values for mucosal area per unit length in young rats with the values for the corresponding regions in the small gut in adult rats as reported by Fisher & Parsons (1950) it appears that the ratios are all significantly lower in the young rat small gut and that an appreciable error could occur if the adult values were applied to young