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Ox red blood cells sensitized with rabbit anti-ox red cell antibody adhered opsonically to freshly prepared human peripheral blood lymphocytes. When tested by a centrifugation technique 24–59% of live lymphocytes in normal individuals formed rosettes with the indicator red cells while 41–87% of the lymphocytes in chronic lymphatic leukaemia reacted. After storage at + 4 °C the lymphocytes gradually lost the operative receptor; killing the cells by freezing and thawing, by sodium azide or by fixation in formaldehyde also resulted in loss of capacity to bind the indicator cells. Pretreatment of the lymphocytes with high doses of anti-human IgM in diluted serum resulted in a definite, although incomplete, inhibition. Also, soluble antigen-antibody complexes were inhibitory, although strong inhibition was difficult to show. Undiluted, heated normal human or rabbit serum was highly inhibitory. The high incidence of lymphocytes showing antibody opsonic adherence in patients with chronic lymphatic leukaemia, together with the finding that most lymphocytes binding sensitized ox red cells did not bind unsensitized sheep red cells (a possible T-cell marker) suggests that lymphocytes showing antibody opsonic adherence represent a subpopulation of peripheral blood lymphocytes. This subpopulation might be an analogue of the B-cell population in mice.

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SUMMARY Cows' milk-fresh, boiled, and processed in different ways for the domestic market, and various infant milk formulae-was investigated for its sensitising capacity in the guinea-pig after being fed for 37 days. The anaphylactic sensitising capacity was considerably reduced by heat-treatment. As heat becomes more intense and more prolonged so P-lactoglobulin and casein become less sensitising. It should be stressed that these were results from experiments on guinea-pigs drinking milk. Should they be found to apply to the human infant too, it seems that it would not be impossible to manufacture a non-sensitising but fully nutritive milk product. The sensitising capacity of fresh and boiled goats' milk was examined too, and it was found that boiling reduced the sensitising capacity to an even greater extent than was the case with cows' milk.

MOLYBDATE AND HYDROLYSIS OF PHOSPHATES 745 3. It is suggested that the effect is due to three factors. (a) If magnesia mixture is added to the reduced phosphomolybdate complex and the resulting precipitate analysed colorimetrically, recoveries of inorganic phosphate are low. (b) Free molybdic acid is reduced, giving molybdenum blue. Contrary to prevailing opinions, molybdenum blue is extracted from acid solutions by i8obutanol. (c) The specific extinction coefficient is about 4-5 times higher when the colour of the reduced phosphomolybdate complex is developed at 1000 than when it is developed at room temperature. This is true for most reducing agents except stannous chloride, with which a higher extinction is obtained at room temperature. 4. The effect is not observed under the milder experimental conditions of Weil-Malherbe & Green (1952). If it had occurred, a stannous chloride method of phosphate estimation, such as was used by these authors, would have been less subject to error than a method using aminonaphtholsulphonic acid. The author is indebted to Mr R. H. Green for much technical assistance.

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