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The Editors do not hold themselves responsible for opinions expressed by their correspondents. No notice is taken of anonymous communicationsA New Blood-Group Antibody, Anti-Jkb THE human blood-group system called Kidd was discovered in 1951 by Allen, Diamond and Niedziela. 1 , who found an antibody, anti-Jkn•, which distinguished two phenotypes, Jk(a +) and Jk(a-).Family investigations• showed that the antigen Jk'' is inherited and that the gene Jka is capable of expressing itself in single and in double dose ; the existence of an allelomorphic gene Jkb was assumed. In tests on 390 rmrelated persons•, the phenotype frequencies were Jk(a+) 76•92 per cent and Jk(a-) 23•08 per cent, from which the following gene and genotype frequencies were calculated : Genes Jk" 0 •5196 JJ.,.b 0•4804 Genotypes Jk"Jk" 0 •2700 Jk•Jk,b 0•4992 J~Jkb 0•2308

Nomi 1215 although simpler to perform, has given too many equivocal results to be satisfactory. It has also given more false positives and false negatives than the quininium test. It is true that we checked it against the much more stringent augmented histamine test, but this would not explain the false positives. There is evidence that if tubeless gastric analysis is repeated in cases in which an equivocal result has been obtained, a definitive result may be obtained in the second test (Flood et al., 1953; Galambos and Kirsner, 1955; Sievers and Gieselman, 1956). It has also been suggested that histamine should replace caffeine benzoate as the gastric stimulant in tubeless gastric analysis. Indeed, Galambos and Kirsner (1955) found only one false positive and one false negative among 104 patients using betazole hydrochloride (" histalog ") instead of caffeine in the azure A test. We are, however, interested in a simple test for achlorhydria which can be performed at home by the patient, and the introduction of parenteral histamine would take tubeless gastric analysis out of the category of screening tests. The exchange-resin methods have no value as quantitative tests of gastric acidity, as the amounts of cation displaced from the resin, absorbed from the intestine, and excreted in the urine are not directly proportional to theamount of hydrochloric acid secreted by the stomach (Segal et al., 1955; Galambos and Kirsner, 1955; Sievers and Gieselman, 1956). The resins are therefore of little use in the study of hyperchlorhydria and peptic ulceration. Their role is in the detection of diseases associated with achlorhydria, such as pernicious anaemia and gastric carcinoma. Summary The literature on tubeless gastric analysis is briefly reviewed and the circumstances under which such tests are likely to be unreliable are mentioned. The quininium resin test was compared with the single-dose histamine test meal in the recognition of achlorhydria; agreement was satisfactory. The azure A resin was compared with the augmented histamine test. The results were unsatisfactory, as there was too high a proportion of equivocal results. In addition, false positive and false negatives were more frequent than in the quininium test. The quininium test is a valuable method of screening patients for achlorhydria, but the azure A method, although simpler to perform, cannot be recommended. We thank Dr. Sheila Callender for her help and Mrs. Allison Jones and Miss Sandra Reynolds for technical assistance. We are grateful to Messrs. E. R. Squibb and Sons, Ltd., for putting the exchange resins at our disposal.

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