I have been talking of the little gloom that still lingers in the usually bright and shining outlook on childbirth. There really is not much, but many an unfortunate mother has had her attention called to the threatening clouds. Rarely has she read the reports of lying-in hospitals or the statistics of life insurance companies.
These are about the most cheerful medical writings that I know of. They are testimony to nature’s great desire to perpetuate the race. Once one of the millions of spermatozoa has united with an ovum, pregnancy has begun; and by the time the woman becomes aware of her condition, the odds are overwhelming that she will go safely through labor and possess a healthy child.
The blood of the mother and that of the child do not actually mix, but the blood vessels of the two are separated from each other by the very thinnest of membranes. Only substances that can be carried in solution in the mother’s blood and pass through these membranes can get into the child. Such membranes are present in all living things. They are called semi-permeable. In the lungs, for instance, the air that is breathed in is almost but not quite in direct contact with the blood. Through such membranes the oxygen goes from the air into the blood and carbonic acid gas (that is, carbon dioxide) travels in the opposite direction. The blood and its other ingredients do not pass.
Professor G. W. Corner, who has written a delightful book called Ourselves Unborn, says that he demonstrated the characteristic operation of such a membrane by putting indelible ink into a sausage skin and suspending it in water. The grains of carbon in the ink, too fine to be seen under a microscope, would not color the water as they could not get through the membrane. Then salt was mixed with the ink and in a little while it could be tasted in the surrounding water. This proved clearly that there is a selectivity in these membranes. Those of the placenta can, as it were, choose or change the substances which should pass through.
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WOMEN’S HEALTH