In a previous paper published in this journal, the author reported the results of investigations made for the purpose of finding the innervation of the blood vessels of the human umbilical cord and placenta, and the effects of the autonomic nerve poisons such as adrenalin, pilocarpin, acetyl-cholin, physostigmin and atropin on those vessels were also described. Further researches have been made with some of the nerve-muscle poisons and muscle poisons, in order to study the action of those drugs upon these embryonic blood vessels. The results obtained are as follows: 1. Pituitrin, in low concentration, shows vasoconstrictor action on the arteries of the cord and placenta, by acting on the sympathetic nerve as well as on the muscles of the vessels. In high concentration, it causes those arteries to dilate, chiefly by affecting their muscles. The veins of those organs are dilated by this drug, regardless of the degree of concentration, through the effect produced on the vascular muscles. 2. Tyramin shows vasoconstrictor action on the arteries of the cord and placenta, by affecting on the sympathetic nerves of those vessels, in low concentration, while in a higher concentration, it acts on the muscles. Tyramin, in very high concentration, dilates those arteries, but complete paralysis of the muscles is not likely to occur readily. 3. The effect of nicotin on the blood vessels of the umbilical cord and placenta is to dilate them, and the point where it acts is the muscles of the vessels. 4. Calcium affects the muscles of the blood vessels of the cord and placenta, and the dilatation of the vessels results. 5. Secacornin and Bombelon show vasoconstrictor action on the vessels of the cord and placenta. They seem to act mainly on the muscles, and to some extent on the sympathetic nerve as well. As far as the action on the sympathetic nerve is concerned, secacornin is superior to Bombelou and it manifests constrictor action in all cases. Bombelon, in low or moderate concentration, causes vasoconstriction, while dilatation is effected in high concentration. The effect of Bombelon on the muscles, especially its paralyzing action is stronger than that of secacornin. 6. Ergotinin makes the arteries of the cord and placenta dilate, by affecting the muscles of the vessels. 7. Quinine shows vasodilating action on the blood vessels of the cord and placenta by acting on their muscles. In high cocentration, quinine causes complete paralysis of the muscles. 8. Barium acts on the muscles of the vessels of the cord and placenta, thus causing constriction of those vessels. 9. The action of papaverin on the blood vessels of the cord and placenta is to dilate them by affecting the muscles. Paralysis of the muscles is very easily brought about by this drug. 10. The reaction of the drugs on the blood vessels of the umbilical cord and placenta is generally not very evident. The blood vessels of the cord, and those of the placenta, manifest nearly the same reaction to the drugs above mentioned, but considerable variation in the reactions in the arteries and veins is observed.