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Updated: May 18, 2025
The test was negative after trauma under anesthesia, and after intravenous injections of thyroid extract, of thyroglobin, and of the juices of various organs injected into the same animal from which the organs were taken. Placental extract gave a positive test. The test was sometimes positive after electric stimulation of the splanchnic nerves.
This attachment of the placental vessels to the internal side of the uterus by their own proper efforts appears further illustrated by the many instances of extra-uterine fetuses, which have thus attached or inserted their vessels into the peritoneum; or on the viscera, exactly in the same manner as they naturally insert or attach them to the uterus.
Over the earth generally, however, they were superseded by the placental mammals, which suddenly break into the geological record in the early Tertiary, and spread with great vigour and rapidity over the four continents. Were they a progressive offshoot from the Mesozoic Marsupials, or Monotremes, or do they represent a separate stock from the primitive half-reptile and half-mammal family?
Thus, it is quite conceivable that a pleurodont lizard might have arisen in Madagascar in perfect independence of the similarly-formed American lacertilia: just as certain teeth of carnivorous and insectivorous marsupial animals have been seen most closely to resemble those of carnivorous and insectivorous placental beasts; just as, again, the paddles of the Cetacea resemble, in the fact of a multiplication in the number of the phalanges, the many-jointed feet of extinct marine reptiles, and as the beak of the cuttle-fish or of the tadpole resembles that of birds.
It supposes a gradual elevation in grade of the vertebrate type in the course of ages from the most simple ichthyic form to that of the placental mammalia and the coming upon the stage last in the order of time of the most anthropomorphous mammalia, followed by the human race this last thus appearing as an integral part of the same continuous series of acts of development, one link in the same chain, the crowning operation as it were of one and the same series of manifestations of creative power.
Over fifty years ago, in a memoir on "Placental Phthisis," Sir James Y. Simpson advanced a new idea in the recommendation of potassium chlorate during the latter stages of pregnancy. The efficacy of this suggestion is known, and whether, as Simpson said, it acts by supplying extra oxygen to the blood, or whether the salt itself is conveyed to the fetus, has never been definitely settled.
In the lower and smaller forms of placental Mammals the surface of the cerebral hemispheres is either smooth or evenly rounded, or exhibits a very few grooves, which are technically termed 'sulci,'separating ridges or 'convolutions' of the substance of the brain; and the smaller species of all orders tend to a similar smoothness of brain.
The latter became the servant of the brain and gave the possibility of using tools. But increase in size and activity, and the expense of producing each new individual, led to the adoption of placental development. And the mammal is so complex, the road from the egg to the fully developed young is so long, that a long period of gestation is necessary.
The frequent presence of poisons in the fetal skin demonstrates its physiologic importance. It has probably not a very marked influence on its health. Arsenic is a powerful abortive agent in the guinea-pig, probably on account of placental hemorrhages.
By this circumstance, I imagine, the terminations of the placental vessels are detached from their adhesions, or insertions, into the membrane of the uterus; and the death of the child succeeds, and consequent miscarriage. Of this I recollect a remarkable instance, which could be ascribed to no other cause, and which I shall therefore relate in few words.
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