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THE present communication is an attempt to elucidate certain of the grosser changes in the mineral metabolism of the body during the healing of a fractured bone, and to describe certain of the phenomena associated with tissue injury.Practically all previous investigations have centred round the relative and absolute amounts of calcium and phosphorus in the blood during different phases of the healing process. The results of the various investigators in this field have been very contradictory. Tisdall and Harris [1922] state that, during the second to sixth weeks of the healing of fractures in adults, the phosphorus content of the serum is raised to about that of childhood and that there is a close parallelism between the concentration of inorganic phosphorus and the formation of new bone. This increased concentration of phosphorus begins to decline towards the normal level about the seventh week. The observations of these two workers on the question of the deviations during non-union were not decisive. Eddy and Heft [1923] confirmed this rise in phosphorus in 23 fracture cases, but found a similar rise in 20 cases involving surgical operations and the healing of tissues other than bone. Moorhead et al. [1925] examined a series of 30 fractures. In less than 50 % there was a rise to 5 mg. per 100 cc. serum.Union in some cases was observed with practically no increase of the phosphorus content and non-union in other cases with a high figure. Several cases showed slight variations in the serum-calcium paralleling the phosphorus. Gyorgy and Sulger [1925] found that the normal phosphorus content of 3 mg. per 100 cc. rises to 5-9 mg. during the healing of a fracture, returning to normal after consolidation. When a fracture failed to unite they found that the phosphorus content had not risen. They also found an increase of phosphorus after osteotomies but not after operations on the soft parts. Satanowski [1925] found in dogs a rise of about 1 mg. 3 days after a fracture. The calcium content remained rather irregular, but slightly below normal. Henderson, Noble and Sandiford [1926] examined 20 cases of un-united fracture where the inorganic phosphorus tended to be about the normal adult content. In two cases only

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Because of the complexity of the interactions involved very few attempts have been made to trace the fate of ingested food in the course of its digestion and absorption along the alimentary tract of the ruminant. Elsden, Hitchcock, Marshall & Phillipson (1946) made a comparative study of the weights of the digesta and their dry-matter and volatile fatty-acid content in the consecutive parts of the alimentary tract of four sheep. By means of a lignin-ratio method Hale, Duncan & Huffman (1947a, b) showed that maximum digestion in the bovine rumen was obtained within 1 2 h after feeding and tended to come to a standstill thereafter. They found that during the first 6 h the predominant phenomenon was the rapid disappearance from the rumen of the more soluble nutrients. During the next 6 h after feeding, cellulose was rapidly disintegrated. Under the conditions of their experiment an average of I 1.6 yo cellulose and 9-5 % protein was later released from the food residues in their further passage along the tract. No observations were made on the fate of the digesta in the other parts of the tract. When, therefore, an experiment of one of our colleagues made a number of ewes available we investigated changes in the quantity and composition of the digesta along the alimentary tract, and also changes in each part of the tract with time after feeding. The concentrations of dry matter (D.M.), ash, nitrogen, energy and volatile fatty acids (v.F.A.) were estimated. Such information is fundamental to a more dynamic appraisal of the processes of digestion and absorption. EXPERIMENTALTwenty-four 5-year-old Cheviot ewes which had lambed in spring, 1951, and weighed about 58 kg, were housed in pens and fed on a diet varying in limestone content because they were on an experiment to define calcium requirement for pregnancy and lactation. They were given water ad lib. and the diet was (g/day):