This paper deals with pharmacological studies of the blood vessels of the human umbilical cord and placenta, for the purpose of investigating the innervation of those vessels and their pharmacological reactions, a matter which is as yet not established. In the research on this subject, the following results were obtained: 1. Adrenalin manifests vasoconstrictor action on the arteries of the umbilical cord and placenta, as well as on the vein of the cord. Also this action may be depressed or reversed by the use of atropin or ergotamine. Adrenalin in high concentration causes all of these vessels to dilate, while the vein of the placenta is dilated by adrenalin in any degree of concentration, within the limits of an efficient dose. The constrictor and dilator action of this drug on the blood vessels is understood to be due to the stimulation of the motor and inhibitory fibres of the sympathetic nerve respectively. 2. Acethyl-cholin acts as vasoconstrictor on the arteries of the cord and placenta. This action may be attributed to the stimulation of the parasympathetic nerve, as it is antagonized by a small dose of atropin. This suggests that the arteries of the cord and placenta are innervated by the vasoconstrictor fibres of the parasympathetic nerve. Despite these facts, it was not possible to recognize the vasoconstrictor action of acethylcholin on the veins of the cord. and placenta. Acethyl-cholin in high concentration dilates both kinds of the blood vessels of the cord and placenta. This dilating action is due not to the paralysis of the muscles of the vessels, but probably to the stimulation of the vasodilator fibres of the sympathetic nerve. 3. The action of pilocarpin on the blood vessels of the umbilical cord and placenta is to dilate them, and its point of attack seems to be the vasodilator of the sympathetic nerve. The effect of this drug on the parasympathetic nerve in these vessels was not observed in this experiment. 4. Physostigmin shows itself to be a vasoconstrictor on the vessels of the cord and placenta. It affects the muscles chiefly and the parasympathetic nerve of the vessels to some extent. 5. Atropin by itself does not have any definite action on the vessels of the cord and placenta, but it can depress the effect of acethyl-cholin by a very small dose, and it can also depress or reverse the effect of adranalin by a larger dose. So, it is clearly seen that the parasympathetic nerve and the motor fibre of the sympathetic nerve are paralyzed by a certain concentration of atropin, but the inhibitory fibre of the latter is not influenced by this drug. Atropin in very high concentration dilates these vessels, owing to the paralysis of the muscle. 6. From the facts learned in this research regarding the pharmacological reactions, it may be concluded that the arteries of both umbilical cord and placenta are innervated by the vasoconstrictor fibre of the sympathetic and parasympathetic nerves, and the dilatation of these vessels is controlled by the dilator fibre of the sympathetic nerve. The existence of the constrictor fibre of the parasympathetic nerve in the vein of the cord could not be proved. The sympathetic constrictor in the vein is inferior in its developement to the same in the artery. In the vein of the placenta, it was not possible to confirm the innervation of the vasoconstrictor of either the parasympathetic or the sympathetic nerve. 7. The arteries of the umbilical cord and placenta show similar pharmacological reaction to the drugs. Therefore it may be concluded that they are under the same innervation. The vein of the placenta reacts to the drugs in a somewhat different way from what the arteries do. The action of the drugs on the vein of the cord coincides partly with the action observed on the arteries, and partly with that on the placental vein. 8. These embryonic blood vessels manifest nearly the same pharmacological reactions as in the general blood vessels of the body, though there is more or less difference between them.