Plain Facts for Old and Young

by John Harvey Kellogg

Such curious cases as the Carolina twins and Chang and Eng were formerly supposed to be the result of the union of two separate individuals. It is now believed that they are developed from a single ovum. It has been observed that the primitive trace—described in a previous section—sometimes undergoes partial division longitudinally. If it splits a little at the anterior end, the individual will have a single body with two heads. If a partial division occurs at each end, the resulting being will possess two heads and two pairs of legs joined to a single body. More complete division produces a single trunk with two heads, two pairs of arms, and two pairs of legs, as in the case of the Carolina twins. Still more complete division may result in the formation of two perfect individuals almost entirely independent of each other, physiologically, but united by a narrow band, as in the remarkable Siamese twins, Chang and Eng.

In a curious case reported not a great while ago, a partially developed infant was amputated from the cheek of a child some time after birth.

The precise cause of these strange modifications of development is as yet, in great degree, a mystery.

[Hybrids.]—It is a well-known law of biology that no progeny result from union of animals of different species. Different varieties of the same species may in some cases form a fertile union, the result of which is a cross between its two parents, possessing some of the qualities of each. The mule is the product of such a union between the horse and the ass. A curious fact is that the offspring of such unions are themselves sterile almost without exception. The reason of this is that they do not produce mature elements of generation. In the mule, the zoösperms are either entirely absent or else very imperfectly developed; hence the fact that a colt having a mule for its sire is one of the rarest of curiosities, though a few instances have been reported. This is a wise law of nature to preserve the purity of species.

[Law of Sex.]—If there is a law by which the sex of the developing embryon is determined, it probably has not yet been discovered. The influence of the will, the predominant vitality of one or the other of the parents, and the period at which conception occurs, have all been supposed to be the determining cause. A German physician some time since advanced the theory that the two testicles and ovaries produce elements of different sexual character, the right testicle forming zoösperms capable of producing only males, and the right ovary producing ova with the same peculiarity. The left testis and the left ovary he supposed to form the female elements. He claimed to have proved his theory by experiments upon animals. Even if true, this theory will not be made of practical importance. It is, in fact, nothing more than a revival of an old theory held by physicians who flourished more than two thousand years ago.

More recently another German physician has advanced the theory that the sex may be controlled at will by observing the time of fecundation. He asserts that when fecundation occurs shortly after menstruation, the result will be a female; but if impregnation occurs later in the month, and prior to the three or four days preceding the next menstrual period, a male will almost certainly be produced. This theory was proposed by Prof. Thury of the academy of Geneva, who claims to have thoroughly tested it in a great variety of ways, and always with an affirmative result. Dr. Heitzman, of New York, an instructor in pathological histology, and an eminent physiologist, informs us that he has thoroughly tested this theory, and finds it to be entirely reliable. There are numerous facts which seem to corroborate the truth of this theory, and future investigations may give to it the dignity of an established physiological fact.

[Heredity.]—The phenomena of heredity are among the most interesting of biological studies. It is a matter of common observation that a child looks like its parents. It even happens that a child resembles an uncle or a grandparent more nearly than either parent. The same peculiarities are often seen in animals.

The cause of this resemblance of offspring to parents and ancestors has been made a subject of careful study by scientific men. We shall present the most recent theory adopted, which, although it be but a theory, presents such an array of facts in its support, and explains the phenomena in question so admirably, that it must be regarded as something more than a plausible hypothesis. It is the conception of one of the most distinguished scientists of the age. The theory is known as the doctrine of pangenesis, and is essentially as follows:—

It is a fact well known to physiologists that every part of the living body is made up of cellular elements which have the power to reproduce themselves in the individual, thus repairing the damage resulting from waste and injury. Each cell produces cells like itself. It is further known that there are found in the body numerous central points of growth. In every group of cells is found a central cell from which the others originated, and which determines the form of their growth. Every minute structure possesses such a center. A simple proof of this fact is found in the experiment in which the spur of a cock was grafted upon the ear of an ox. It lived in this novel situation eight years, attaining the length of nine inches, and nearly a pound in weight. A tooth has been made to grow upon the comb of a cock in a similar manner. The tail of a pig survived the operation of transplanting from its proper position to the back of the animal, and retained its sensibility. Numerous other similar illustrations might be given.