The effect of growth and function on the chemical composition of soft tissues

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Abstract
Skin, cardiac muscle, liver, kidney and brain of man and the pig have been analyzed in the foetus, in the new-born, during the suckling period and in the adult. Development was associated with a fall in the proportion of water and an increase in the proportion of nitrogen in all tissues; fetal heart muscle, and foetal liver and kidneys reached their adult composition before skin and skeletal muscle, and it is suggested that this is related to their early functional development. Next to skeletal muscle the skin is the largest soft tissue of the body, and changes in its composition make a significant difference to the composition of the body as a whole. The proportion of collagen per kilogram of skin increased during development, both in absolute terms and as a percentage of the total nitrogen. The cellular constituents were at a maximum at about the time of birth. The hearts of the still-born babies contained considerably less potassium than did the fetal hearts. Two possible explanations are put forward for this anomalous finding. Human brain contained more water and less nitrogen and phosphorus than pig brain at corresponding stages of development. This may be due to a larger amount of grey matter in human brain substance.