In some countries the exhibition of monstrosities is forbidden because of the supposed danger of maternal impression.

The celebrated "Siamese Twins" for this reason were forbidden to exhibit themselves for quite a period in France.
We shall cite only a few of the most interesting cases from medical literature.

Hippocrates saved the honor of a princess, accused of adultery with a negro because she bore a black child, by citing it as a case of maternal impression, the husband of the princess having placed in her room a painting of a negro, to the view of which she was subjected during the whole of her pregnancy.

Then, again, in the treatise "De Superfoetatione" there occurs the following distinct statement: "If a pregnant woman has a longing to eat earth or coals, and eats of them, the infant which is born carries on its head the mark of these things." This statement, however, occurs in a work which is not mentioned by any of the ancient authorities, and is rejected by practically all the modern ones; according to Ballantyne, there is, therefore, no absolute proof that Hippocrates was a believer in one of the most popular and long-persisting beliefs concerning fetal deformities.
In the explanation of heredity, Hippocrates states "that the body of the male as well as that of the female furnishes the semen.

That which is weak (unhealthy) is derived from weak (unhealthy) parts, that which is strong (healthy) from strong (healthy) parts, and the fetus will correspond to the quality of the semen.