1 Department of Biological Chemistry, Harvard Medical School, Boston, Massachusetts
The problem of whether fetal tissues differ either qualitatively or quantitatively in their metabolic properties from adult tissues, and in particular whether they are able to obtain energy more efficiently under hypoxic conditions, has been investigated and discussed in a host of papers and symposia. The question of whether the mammalian fetus normally develops under hypoxic conditions has also been discussed extensively. Many observations relating to these questions have been made using rat or rabbit fetuses and sheep or goat fetuses. In these animals, observations can be made over the entire span of fetal life, but the characteristics of the placentas of these mammals differ in many respects from those of the human placenta and the pattern of development of enzymes in these fetuses is significantly different from the comparable pattern in human tissues.