Richards & Greig (1952) reported pale livers and enlarged flabby hearts in weanling mice whose mothers' diets contained 1-2 % of added calcium carbonate. It seemed likely that the calcium carbonate had induced an unexpected anaemia in the young.The work reported in the present paper was undertaken to investigate this possibility and to examine the pathology of the condition. The presence of anaemia was confirmed by haemoglobin estimations, and fuller examination of the blood indicated that it was probably of the iron-deficiency type. A further experiment showed that the anaemia could be prevented by feeding an iron supplement, but not by balancing the additional dietary calcium with sufficient phosphorus to restore the original Ca: P ratio of the diet. METHODS

Within recent years several experiments on laboratory animals at this Institute have indicated that additions of calcium carbonate to the diet may have deleterious effects. Thus the effects of pyridoxin deficiency induced in suckling rats by excess of aneurin were accentuated when calcium carbonate was also added to the diet (Richards, 1945); when the amount of added CaCO, was increased, there was also a retardation in the rate of growth of young rats after weaning (Richards, 19490). Simpson These observations led to the present experiments, of which the initial object was to test the effects on reproduction in mice of including different levels of CaCO, in the original slightly modified Sherman B diet and at the same time to assess the relative importance of the various changes made in this diet by Howie & Porter (1950).The results of the first experiment indicated that any differences resulting from the other modifications were of minor importance compared with those due to the additions of CaCO,. A second experiment was therefore designed to investigate means by which the deleterious effects of these additions could be counteracted. As the work developed, observations were made indicating that it would be of interest to record the weights of various organs of the young mice and their mothers. These aspects are best considered separately, and the present paper is accordingly presented in two parts: the first deals with reproductive effects and the second with effects on organs.

1. By separating the sources of variability in an experiment involving haematological observations it has been shown how to estimate the usefulness of repeated observations on each animal.2. In the illustration provided it is concluded that when monozygous twin calves are used, random variability accounts for so much of the total variability that a great improvement in accuracy can be achieved by taking repeated observations on each animal. When unrelated calves are used, little additional accuracy is obtainable by taking more than about three observations on each.3. It is shown that, in consequence, the relative efficiency of monozygous twin and unrelated calves is likely to vary, depending upon the number of observations on each animal. Thus, to benefit fully from the increased efficiency offered by monozygous twins, more observations are required on each animal than in the case of unrelated animals.4. Although the figures refer to haematological measurements on calves, the statistical method evolved is of wider application.

Much information is available concerning the influence of specific dietary factors on the cellular elements of the blood, but the practical question of whether the blood of cattle is affected during the rearing stage simply by the quantity of food fed has so far been neglected.The opportunity to investigate this point was provided by a long-term experiment in progress at this Institute, aimed at determining the effects of high and low planes of nutrition during the rearing stage on the subsequent growth and performance of dairy cattle. This experiment-of which only preliminary accounts have as yet been published (Crichton, 1953;Crichton & Aitken, 1954)-involves the use of monozygous twin calves, and for this reason it also enabled us to compare monozygous twins and unrelated animals in respect of their efficiency for haematological studies.Our investigations have shown that a high plane of nutrition can result in a distinctly improved blood picture, and also that the use of monozygous twins for this type of study leads to a marked increase in efficiency. MATERIALS AND METHODSMeasurements were made on the blood of eight pairs of monozygous twin heifer calves. Two pairs were on a high plane of nutrition, two pairs were on a low plane, while one member of each of the remaining four pairs was on the high plane and the other on the low plane. All the calves were cross-breds, but of mainly dairy type, and at the time of examination all were between 7 and 9 months of age.The high-and low-plane rations had been designed to correspond with 110 and 70 % respectively of the Ragsdale standard (for details see Crichton & Aitken, 1954). All the calves were reared on milk or milk substitutes up to 3 months of age, when they were weaned on to a diet of hay, turnips and concentrates, the differences in the rations fed being quantitative only. At 6 months of age the concentrate supplement was withdrawn from the lowplane animals, while calves on the high plane of nutrition continued to receive 2 lb./day.The haematological observations were conducted

The clinical and pathological features of a case of chronic nephritis in a 17-year-old pony was described. Measurement of fluid intake and laboratory analysis of sequential blood and urine samples helped in establishing an accurate diagnosis. The case demonstrates that although chronic renal disease is not well documented in the horse it should nevertheless be considered in the differential diagnosis of conditions characterised by progressive loss of weight.