Fourteen days of static weight maintained by limited caloric intake reduced the neutral salt-extractible collagen to very low levels. Following this period, 5 to 7 days of steady weight gain induced by ad lib. feeding was required to produce significant increases in this collagen fraction. Return to control levels occurred within 12 days of continuous growth.

The amount of collagen extracted from the dermis of young guinea pigs with cold neutral salt solutions varied directly with growth rate (weight gain) and was greatly diminished after short periods of restricted caloric intake. Two days of fasting diminished the total extracted collagen by one-half.

Three consecutive extractions with citrate buffer pH, 3.5, of the residues remaining after exhaustive saline extraction removed 40 per cent more collagen from the skins of actively growing animals than from those of animals fasted for 2 days. However, subsequent extraction of residues with dilute acetic acid equalized the total amount of collagen extracted at acid pH from the two groups.

The viscosity of cold neutral extracts was unrelated to the concentrations of non-collagenous proteins and carbohydrates but varied directly with the collagen content.