The development of motor responses in the stomach of the foetal sheep.

Knowledge of the movement of the gut in the mammalian foetus is mainly derived from observations on small laboratory animals. Yanase (1907) made a systematic study of pre-natal intestinal movement in the guinea-pig, and observed that the appearance of peristalsis coincided with the time of development of the longitudinal muscle of the gut, at about the 27th day of gestation. At the stage when circular muscle alone was present, he was able to elicit only local constriction by mechanical or faradic stimulation. Foetal gastric movement was observed in the rabbit (Tani, 1927) and in the cat by Friedman (1934), Windle & Bishop (1939), and Becker & Windle (1941). The last-named described rhythmic and persistent gastric peristalsis in cat foetuses of 35-40 days. Becker, Windle, Barth & Schultz (1940) found that thorotrast injected into the amniotic sac of the guinea-pig circulated through the alimentary tract of the foetus from the 42nd day onwards; and human foetal swallowing is said to occur from the fifth month (Windle, 1940). While there is evidence, therefore, that alimentary tract movement commences in pre-natal life, nothing is known of the factors controlling the onset of movement or of the nature of the individual movements. The movements of the stomach of the foetal sheep are described here, as this species might be expected to yield more evidence than others concerning the spontaneous occurrence of movement, the nature of the movement, and the part played by the vagus in initiating it, for in adult ruminants the movements of the parts of the stomach are characteristic and marked. Further, Barcroft & Barron (1939) observed swallowing and suckling movements in the foetal sheep, and as suckling in the lambs is associated with a reflex closure of the structure known as the oesophageal groove, the onset of the reflex in foetal life can be expected to provide some index of the post-natal activity.