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Sheep foetal weight and length data have been collected for the purpose of checking foetal age and in the course of this work it has been found that the cube root of the foetal weight gave a linear plot with age from the 50th day of pregnancy to full term. The purpose of this paper is to describe this result and to indicate how the cube root relationship may be extended to other mammalian data, and to discuss its significance in comparative foetal physiology.Early attempts to find empirical formulae relating foetal weights to age from conception have been extensively reviewed by Needham (1931). The majority of these involved a linear relationship between weight and a power (approximately the third power) of the time or, alternatively, a relation between time and a cube or higher root of the foetal weight.Greater precision was brought to such formulae by McDowell, Allen & McDowell (1927) who introduced the concept of embryo age and obtained a formula, essentially of the power type, relating log weight and log embryo age. The embryo age was arbitrarily determined to commence with the appearance of the primitive streak (7.2 days for mouse embryos, 12 days for guinea-pigs), and the powers obtained varied from 3-65 to 3-99 for the mouse and guineapig respectively.The power obtained in this way is very sensitive to small changes in the arbitrarily fixed zero embryo age which has no sound physiological basis.If a steady state of growth exists during foetal development one would expect it to be most free from complications when the foetus has the environmental stability such as provided by an established placental circulation. It would be an advantage therefore if weight and age data for the last half or two-thirds of pregnancy could be represented without using the arbitrary expedients necessary with logarithms.This problem faced us in our endeavour to obtain a representation of collected data of weights and lengths of foetuses from Welsh ewes, which could be used for checking foetal ages.

In 1949 Barklay, Haas, Huggett, King & Rowley recorded the fructose and non-fructose reducing substances in the amniotic and allantoic fluids and the blood of the sheep foetus. This paper records experiments designed to ascertain the origin of the blood fructose of the foetal sheep.t In the 1949 paper Barklay et al. recorded the literature. To the points given there it is worth adding that Bacon & Bell's (1948) isolation and identification of the Seliwanoif-positive ketose as D-fructose was accompanied by proof that the only reducing sugars in the foetal blood were D-glucose and D-fructose. On the other hand, Karvonen (1949a) has shown, using Cole's method (1948), that human cord blood contains no fructose, a result at variance with that of Orr (1924). In 1949 Hitchcock, in a paper marked by pronounced technical accuracy, recorded the levels of fructose and glucose in the foetal and maternal bloods of sheep in the second half of gestation, together with their distribution between corpuscles and plasma. He confirmed more definitely the findings of Barklay et al. (1949) that the fructose of the foetal blood has its highest values in early pregnancy and tends to fall as intrauterine growth proceeds. In addition, he found that glucose traversed the placenta from the mother to the foetus, and he regarded the maternal loss and foetal gain as equivalent. The fructose problem can be posed in the form of three questions. (i) What is the site of the formation of fructose? (ii) What substance gives rise to fructose? (iii) What is its role in the foetus? The experiments in this paper were designed to obtain answers to the first two questions. The relation between the maternal and foetal blood sugars is of primary * Formerly N. V. Winterton. t A preliminary note appeared in Nature (Huggett, Warren & Winterton 1949a) and a communi. cation was given to the 1st International Congress of Biochemistry (Huggett, Warren & Winterton, 1949b). FRUCTOSE IN THE FOETAL SHEEP 259 importance. All evidence, both experimental and clinical (diabetes), goes to show that high maternal blood sugars are accompanied by high foetal blood sugars. Indeed, Passmore & Schlossmann (1938) found that, on injecting glucose into the maternal circulation of goats and sheep, the foetal blood sugar rose to higher levels than the maternal blood sugar. In all their experiments the blood sugar was estimated as glucose. The possibility existed that the apparent excess of foetal glucose over maternal glucose might be due to fructose being formed which was falsely estimated as glucose, the true foetal glucose being actually less than the maternal glucose. In the experiments of this paper the foetal blood glucose and fructose have been determined simultaneously, and they start from the repetition of Passmore & Schlossmann's work on the intravenous injection of glucose into the maternal circulation. METHODS These were essentially the same as described in Barklay et al. (1949). Welsh ewes ofknown conceptual date were received in the laboratory 1 or 2 days before the ex...

The numerous data in the International Whaling Statistics relating foetal length to date of catch have been studied. They can be used as alternatives to cube roots of foetal weights to give rates of foetal growth and for the computation of data of conception and foetal ages. There are major differences between the Mysticeti and Odontoceti. The main gestation period for the former is 10.8.±1‐2 months and for the latter 14 ± 2 months. In both groups the greatest birth‐weight is attained by an increased foetal growth rate, to such an extent in the rorquals that the gestation period in the largest is actually shorter than in the smaller species. There are dietetic and metabolic differences between the two sub‐cohorts. The outstanding one is that pregnant mysticetes appear to stop feeding and lose body fat to the foetus during late pregnancy, at the time when the foetal increase in size is maximal. The causes of the differences in growth and metabolism of the two groups are unknown, apart from those imposed by differences in their ecology.

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