FOR convenience this paper will be divided into two sections, the first dealing with the cholesterol content of normal tissues in the rabbit, and the second with such modifications as were produced by intravenous injections of cholesterol.The first section was undertaken with the object of obtaining such light on the physiology of cholesterol as could be derived from a rough comparison of the cholesterol content of different tissues, and also of providing adequate controls to the experiments in Section II. The second section was expected to give information on problems of storage and metabolism, and the part taken by different organs in these processes.

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IT has been known for a considerable time that variations in blood cholesterol occur during pregnancy, and it was not entirely unexpected therefore when the sex differences in the cholesterol content of tissues to be described here were demonstrated. These sex differences were discovered during the examination of a large number of normal rabbits (8), when it was desired to have estimations of the cholesterol content of various tissues for purposes of control.Before including both sexes in the series of controls, it was considered advisable to determine whether or not any material differences existed between the two sexes. Experiments soon showed that such differences did exist, and doe rabbits were discarded for control purposes, but the differences noted were deemed worthy of further investigation.The results of this investigation are set forth here, together with the influence of pregnancy on the differences described.Experimental. The aniimals used were rabbits and the tissues examined included suprarenals, ovaries, spleen, kidney, liver and brain. The procedure and method of estimation of cholesterol were similar to those previously used and described (8), but it must be emphasized again that with the method used only gross variations (over 20 p.c.) have been regarded as significant.Results. These may be considered under the headings of the different organs and tissues, and the details are set forth in tabular form.All figures refer to "total cholesterol," i.e. to free and combined cholesterol estimated together. This, admittedly, is not so satisfactory as having separate estimations of the free and ester cholesterol, but nevertheless the results obtained are significant both in themselves and as affording guidance to more detailed study, and the simplicity of the procedure has enabled a much larger number of experiments to be made than would otherwise have been possible.

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