My research interests have been in the area ofperinatal physiology, and specifically in the nutritional requirements and metabolic charac-teristics ofthe mammalian fetus and newborn. Over the years, we have defined the" fetal diet" represented by the umbilical uptake of nutrients for the ovine fetus (1, 2). Unfortunately, this remains the only description available forany mammalian species to date. This dietary intake is composed primarily of amino acids and carbohydrates including glucose and lactate. This composition is in striking contrast to the intake ofbreast milk which in all mammals, including man, represents a striking change to a high fat diet.

There is a remarkable diversity among mammals in the manner in which the metabolic demands of pregnancy and lactation are met. In some species such as the rabbit, most ofthe increase in maternal metabolic demands required to produce an independent young occurs during lactation. In others, such as the guinea pig, most of the growth occurs in utero, and pregnancy is the time of greatest metabolic demand. Mammals also show great diversity in the size of the newborn produced with respect to the mother's body size, as well as in the length of time it takes to build a newborn (gestation length). For example, in bears, the newborn weight is less than 1% of the mother's pre-pregnancy weight and in bats, the metabolic demands of pregnancy are so great that the usual sexual dimorphism is reversed, with the female larger than the male, and the degree of difference is a function of the litter size of the species. One ofthe first studies we carried out several years ago, when it first became possible to catheterize the mid-gestation fetal lamb, was to examine the allometric relationship between oxygen consumption and fetal size from mid to late gestation (3, 4). Figure 1 presents these data. The figure clearly demonstrates that oxygen consumption does not