Osborne and Mendel fed young rats on diets which were fairly satisfactory in their composition with respect to all factors other than protein. Their content of protein was below the amount which would suffice for the support of growth. The animals restricted to such food supplies remained stunted for long periods and yet were able, when later the amount of protein in their diets were increased, to resume growth at rates which the experimenters regarded as faster than rats ordinarily grow on a "normal" diet. From these results the deduction was drawn that interruption of growth does not result in the loss of the capacity to grow (46).

This generalization is too sweeping. It is true that rats which are stunted by means of protein starvation retain for long periods their capacity to resume growth and of a fairly normal character, the form of the grown animal being more or less closely similar to that of animals whose growth to adult size has been uninterrupted. McCollum and Simmonds (46) have found that rats which are at an early age kept upon diets in which the inorganic content is unsatisfactory, develop abnormal forms, and become permanently stunted. They become stocky, owing to failure to grow in length. Such animals may grow to a slight extent if their diet is later made satisfactory, but they always remain deformed. Any nutritive regimen which will induce rickets will, they find, markedly interfere with subsequent growth, when later, the faults in the diet are corrected.

Animals, whose growth has been suspended by depriving them of fat-soluble A, or water-soluble B, are able to resume growth upon the inclusion of the missing complex in the diet. It is not possible, however, to carry animals on such diets for long periods, because of the disaster which inevitably befalls them.