1. Sialic acid has been found to interfere with three colorimetric reactions used for the estimation of DNA: a modified diphenylamine reaction at 100 degrees (Dische, 1930), the nitrophenylhydrazine method (Webb & Levy, 1955) and the diphenylamine reaction at 30 degrees (Burton, 1956). 2. Evidence is presented that sialic acid is present in hydrolysates obtained from gastric wash-out material. 3. A mathematical method for correcting for interference from sialic acid in the diphenylamine reaction at 30 degrees is described. 4. The diphenylamine reaction has been modified to make it suitable for the estimation of DNA in the presence of sialic acid. The modifications are to increase the concentration of diphenylamine to 2% and to perform the reaction at 6-13 degrees for 48hr. These modifications increase the sensitivity 25% above Burton's (1956) modification of the diphenylamine reaction. 5. The precipitation, extraction and recovery of DNA from gastric wash-out material have been investigated.

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SYNOPSIS A method is described for the direct colorimetric determination of urea in biological fluids. The method depends on the reaction (first described by Wheatley, 1948) between urea, diacetylmonoxime, and phenylanthranilic acid in the presence of controlled amounts of oxidant; chloride ions are included to sensitize the reaction; manganous ions stabilize the resultant colour; and phosphate enables reasonable reproducibility to be achieved.The method is rapid and suitable for routine analytical purposes. Precision and accuracy are good; sensitivity is high for an activated acid reagent up to about one week old, and thereafter decreases.A hypothetical mechanism for colour formation is presented.Of the numerous methods published for the direct colorimetric determination of urea and its derivatives, the most investigated have been those based on the Fearon (1939) carbamido reaction between the urea compound and diacetyl monoxime (DAM), iso-nitrosopropiophenone, or diacetyl (Ormsby, 1942; Barker, 1944;Archibald, 1945; Wheatley, 1948;Natelson, Scott, and Beffa, 1951; Friedman, 1953;Koritz and Cohen, 1954;Rosenthal, 1955; Kawerau, (1946); Marsh, Fingerhut, and Kirsch, 1957;Le Mar and Bootzin, 1957;Sardou, 1958;Girard and Dreux, 1958;Crokaert and Schram, 1958;Holden, 1959). The number of attempts which have been made to meet the difficulties encountered is indicative of the magnitude of the problem. The disadvantages which have to be overcome include the instability of the resultant colour to light and time; the differential effect of light on blanks and test solutions; low to moderate sensitivity; prolonged heating time for reaction; sensitivity of colour intensity to reaction temperature; the objectionable nature ofthe reagents, e.g., concentrated hydrochloric acid, arsenic compounds; lack of proportionality between urea concentration and colour over a sufficiently wide range.The present work is an attempt to develop reagents which minimize or obviate these various disadvantages. A discussion of the chemistry of the reactions involved is given.

Part I Cell loss in rats with a normal mucosaThe concept of continuous epithelial renewal in the gastrointestinal tract was introduced at the end of the nineteenth century (Patzelt, 1882;Bizzozero, 1888;Schaffer, 1891), and since then labelling experiments with tritium-labelled thymidine have established that epithelial cells are produced in the crypts of the small intestinal mucosa, migrate up onto the villi and are lost at the tips, both in experimental animals (Leblond and Messier, 1958;Quastler and Sherman, 1959;Creamer, Shorter, and Bamforth, 1961) and in man (Shorter, Moertel, Titus, and Reitemeier, 1964;MacDonald, Trier, and Everett, 1964). It has been previously considered that epithelial cells migrate up from the mouth of the crypts directly onto villi on all sides, and it has therefore been assumed that there is an orderly one-to-one relationship of crypts to villi, with one crypt orifice between adjacent villi. In another communication (Loehry and Creamer, 1968) we have established that the crypt-villus relationship in the small intestinal mucosa is more complex than has been assumed, that overall there are many more crypts than villi, that very few of the crypts open out onto villi on all sides, and that, in most cases, much of each crypt opening is adjacent not to villi but to other crypts. The migration therefore of epithelial cells from crypts to villi cannot be a simple direct progression as might be expected from two-dimensional sections. Two possibilities exist: those cells emerging at sites where two crypts are adjacent must either be desquamated here at the crypt mouth or else be channelled round in some way onto villi. Because of this complex crypt-villus relationship it was thought necessary to undertake a reappraisal of cell migration, and, in order to establish whether cells were desquamated at the crypt mouth or channelled onto villi, to study the problem by a consideration of cell loss. METHODS AND TECHNIQUESDesquamated epithelial cells were collected from male 13 albino rats by total small intestinal perfusion. The animals were anaesthetized with intraperitoneal nembutal and the abdomen was opened by a midline incision. A length of 1 mm diameter PVC tubing was passed through the mouth into the rat's stomach, and guided through the pylorus into the fourth part of the duodenum where it was tied by a silk ligature. Another piece of PVC tubing, 4 mm in diameter, was passed through a small incision in the caecum and tied in place in the distal ileum. This cannula passed directly into a collecting bottle. It was found that this method of cannulating the small intestine prevented any significant bleeding into the lumen, and when the tubes were in position the small bowel could be perfused without contamination from the stomach, gallbladder, or pancreas. The small intestine with the cannulae was returned to the peritoneal cavity and normal saline infused via a constant flow pump at a temperature of 37°C. Perfusions were performed at a rate of 250 ml per hour after an initial washout, and hourl...

It has been established practice for 60 years to prepare thyrotoxic patients undergoing thyroidectomy with Lugol's iodine. However, evidence in support of its claimed benefits, namely a reduction in the vascularity and friability of the toxic thyroid gland, is scanty. We have therefore determined the effect of Lugol's iodine on thyroid blood flow, as measured by thyroid uptake of thallium-201, in nine patients with Graves' disease and one euthyroid patient. Thallium-201 uptake, as well as serum thyroxine and triiodothyronine, fell significantly after treatment with iodine. Although not correlated with thyroid function tests, thallium-201 uptake was significantly correlated with thyroid weight. These results support the contention that thyroid blood flow is reduced in thyrotoxic patients treated with Lugol's iodine.

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