These studies were undertaken in order to determine whether or not there is an increase in the water content of the blood during the rapid gains in weight which not infrequently occur in healthy, artificially fed infants. Freund1 has shown that these large weight increases are due to water retention. He studied the nitrogen and chlorid balance in a series of artificially fed infants and found that during the days of rapid gain the nitrogen retention was sufficient to account for only a small part of the increase in weight. That the major part was due to water retention was shown by the marked diminution in the elimination of chlorid and alkali salts.
In these studies the refractometric method was used to determine variations in the blood water. The technic employed was similar to that described in previous papers.2 The serum proteins were calculated from the refractive index of serum