No abstract

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.

Previous experiments (Richards, 1945) showed that excess of vitamin B, in a diet rather low in the vitamin B complex caused deficiency of another vitamin B factor, pyridoxin. The deficiency, which appeared to be accentuated by addition to the diet of calcium carbonate (chalk), became manifest during the lactation period, when the suckling young developed convulsive fits characteristic of pyridoxin deficiency. No evidence of the deficiency had been apparent during the growth of the young rats before mating. It was decided, therefore, to increase the intakes of vitamin B, and chalk still further, in order to find whether the resulting accentuation of the dietary imbalance would elicit obvious differences between the groups of animals during their growth. From this experiment arose the present series of investigations dealing mainly with the effect of pyridoxin on the thymus development of suckling rats, under conditions of pyridoxin deficiency induced by excessive amounts of vitamin B, in the diet.A short account of part of the present investigation was communicated to the Biochemical Society (Richards, 1946).Since the growth test with the increased intakes of vitamin B, and chalk still showed no obvious differences between the groups, the animals were mated to find whether these increases would accentuate the effects previously observed on breeding and lactation. While the breeding tests were in progress, Stoerk & Zucker (1944), who had fed young rats after weaning on diets lacking in one or other of four vitamin B factors, reported atrophy of the thymus after 4 weeks of experiment, the atrophy being greater when pyridoxin was lacking than when vitamin B, , riboflavin or pantothenic acid was absent. This suggested that the conditioned pyridoxin deficiency produced by excess of vitamin B, might have an effect on the development of the thymus gland in the stage before weaning. The thymus glands of the young rats in subsequent litters were accordingly weighed at weaning. When it became evident that pyridoxin had a marked effect in preventing atrophy of the thymus in the young rats, a further experiment was made to determine whether this effect was specific for pyridoxin, or whether a similar result would be obtained by the addition of any other single vitamin B factors to the diet, unbalanced by its excessive content of vitamin B, . The specificity of pyridoxin for thymus development in young rats after weaning was proved by Stoerk in a later paper (Stoerk, 1946).

Basic Properties of Oxygen in Organic Acids and Phenols; and the Quadrivalency of Oxygen.

No abstract