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SUMMARY Absolute and relative growth curves have been determined for the cerebellum and whole brain of the pig foetus from 45 days to term, using fixed material. They have been related to conceptual age and a newly calculated body length curve. Equations are given for predicting (a) conceptual age from crown-rump length, and (b) cerebellum:brain ratio from either conceptual age or crown-rump length.

In a study of individual differences in neonates, frequencies and durations of spontaneous visual alertness were recorded and visual pursuit was measured in 32 2- to 3-day-old healthy neonates. Rank correlations of .60, .65, and .74 between the three visual measures suggested that infants who alerted frequently tended also to be the infants who alerted longest and who were most capable of visual pursuit. The results showed not only this intra-individual stability in the visual behaviors but also high variance between infants in their capacity for visual alertness. The infants' sex, parity, birthweight, estimated conceptual age, and postnatal age were not significantly related to the capacity for visual alertness, nor were the moderate levels of obstetric sedation used in this sample. The three visual measures, while tapping a shared capacity, had different correlates. Frequencies and durations of visual alertness were significantly related to a number of variables which had in common, moderate degrees of underlying activation and arousal. These factors did not contribute to visual pursuit. Sensitivity to auditory stimuli was significantly correlated with the capacity for visual pursuit but was unrelated to other visual measures.

The mean concentration of citric acid in male and non-pregnant female adult guinea pig plasma was 0.308 ± 0.042 mM. Pregnant females with fetuses of 49–69 days gestational age had mean maternal and fetal plasma concentrations of 0.440 ± 0.011 and 0.217 ± 0.053 mM, respectively. Maternal and fetal values were not correlated. Neonates up to 96 h old had plasma citrate values similar to those in the fetus. The citrate concentration of the amniotic fluid was lower than that in fetal plasma and showed a negative correlation with conceptual age (p < 0.01).

The “electroencephalographic age” presents an independent parameter for the estimation of the maturational stage of the newborn infant comparable to the determination of bone age by x-ray. Measurements of photically evoked responses render the electroencephalographic method more objective than visual inspection of the electroencephalogram pattern alone. The method is as harmless as translumination by flashlight and can be carried out in the nursery for premature infants by using transportable instruments.

Plasma from six chronically catheterised sheep fetuses of 113–126 days conceptual age showed high levels of corticotrophin at all ages with somewhat higher values towards term. Plasma cortisol was not clearly related to corticotrophin in individual samples but was highly correlated in the pooled data. Short bouts of hypoxia (5–10 min 10% O2 in N2 to the mother) produced no significant change in either corticotrophin or cortisol although small transient changes in PO2 and lactate occurred. The high levels of corticotrophin suggest that the possibility of stress in the chronically catheterised preparation must be considered.

The effect on plasma insulin of elevating plasma glucose levels was studied in exteriorized sheep fetuses of 68 to 142 days conceptual age and in 2 lambs, 1 and 7 days old. Fetuses of less than 110 days showed, at most, only a very small and delayed rise in plasma insulin following an injection of glucose (1.67–3.45 g/kg body weight) into the umbilical vein. In 5 out of 6 fetuses of 110 days and older intravenous glucose (0.54–1.38 g/kg) was followed by a marked but delayed rise in plasma insulin reaching a peak 25–100 min after glucose administration. In the lambs intravenous glucose (1 g/kg) gave an immediate response in plasma insulin. Intraduodenal glucose was also seen to give a marked rise in plasma insulin in a 123 day fetus and 2 lambs. Intravenous fructose (0.65 and 0.55 g/kg) to two older fetuses caused no rise in plasma insulin although glucose given subsequently evoked a marked response. The onset of appearance of a marked response to glucose in the fetus was preceded by a proliferation of secondary islets in the pancreas. The changes in plasma insulin in the exteriorized fetuses and in 2 isolated fetuses suggest that the placenta must be relatively impermeable to insulin, fetal insulin must largely be derived from the fetal pancreas and fetal tissues must take up insulin.

The developmental progress of 68 (94%) of 72 surviving infants born during 1966-69 who weighed 1500 g. (3 lb. 4 oz.) or less at birth has been assessed at follow-up. At a mean conceptual age of 2 years 3 months (range 9 months to 4 years 3 months) 59 (86.7%) appear to be normal children, 5 (7.4%) are abnormal, and 4 (5.9%) are classified as " doubtful ". These results suggest that the prognosis for infants of very low birth weight has improved following the introduction of modern methods of care.