One of the interesting results of the experiments was the production of a number of intersexual types of various grades. This was easily verifiable by colour and other characteristics. To make sure that the instincts were correspondingly modified, behaviour was registered on moving-picture films. Where the first egg of a clutch (the one with a small, normally male-producing yolk) produces a female, she is usually found to be more masculine than her sister from the second egg with the larger yolk. This is true both as to appearance and as to behaviour. Some of these were quite nearly males in appearance and behaviour, though they laid eggs.
Testicular and ovarian extracts were injected. The more feminine birds were often killed by the testicular extract, the more masculine by the ovarian extract. Finally, to make assurance doubly sure, some females which should theoretically have been the most feminine were dissected and shown to be so. That is, out-crosses which produced a predominance of females in the fall were mated with females which had been overworked at egg production until they threw nearly all females. Dissecting the females thus produced, they were shown to have right ovaries, which means double femaleness, since normally the pigeon is functional only in the left ovary, like other birds. The right one usually degenerates before or at hatching and is wholly absent in the week-old squab.
In pigeons, Riddle thinks the "developmental energy" of the eggs is in an inverse ratio to their size. The last and largest eggs of the season develop least and produce most females. The second egg of a clutch is larger than the first, but develops less and the bird produced is shorter-lived. Overworking and other conditions tending to produce large eggs and females also throw white mutants and show other signs of weakness. Old females lay larger eggs than do young ones. These eggs produce more females. They store more material, have a lower metabolism and less oxidizing capacity than do the earlier male-producing eggs.
It would be unsafe to draw specific conclusions about mammals from these bird and insect experiments. Both the secretory action and the chromosome mechanisms are different. The quantitative nature of sex, and also the existence of intersexual types, between males and females, would seem to be general phenomena, requiring rather slight corroboration from the mammals themselves. We have such mammalian cases as the Free-Martin cattle, and some convincing evidence of intersexuality in the human species itself, which will be reviewed presently.
The notion of more "developmental energy" or a higher metabolism in males is borne out in the human species. Benedict and Emmes [[7]] have shown by very careful measurements that the basal metabolism of men is about 6% higher than that of women. Riddle cites the work of Thury and Russell on cattle to show that a higher water value (as he found in the pigeon eggs), associated with increased metabolism, helps to produce males.
In males, the secretion of the sex glands alone seems to be of particular importance, again suggesting this idea of "strength" which comes up over and over again. Removal of these glands modifies the male body much more profoundly than it does the female. [[8]] It is quite generally supposed that the action of this one secretion may have much to do with the superior size and vigour of males. For example, Paton says [[9]]: "The evidence thus seems conclusive that in the male the gonad, by producing an internal secretion, exercises a direct and specific influence upon the whole soma, increasing the activity of growth, moulding the whole course of development, and so modifying the metabolism of nerve and muscle that the whole character of the animal is altered." It used to be said that the male was more "katabolic," the female more "anabolic." These expressions are objectionable, inasmuch as they hint that in a mature organism, with metabolism rather stable, tearing down, or katabolism, could go on faster than building up, or anabolism, or that one of two phases of the same process might go on faster than the other. It seems safer to say merely that a lower metabolism in the female is accompanied by a tendency to store materials.
A long time will doubtless be required to work out the details of differences in metabolism in the two sexes. Some of the main facts are known, however, and the general effects of the two diverse chemical systems upon the life cycles of the sexes are quite obvious. What we call the "quantitative theory of sex" has, besides a place in exact science, an interesting relation to the history of biological thought, especially as applied to society. It is thus in order to state as clearly as possible what it now is; then, so that no one may confuse it with what it is not, to run over some of the old ideas which resemble it.
Experiments with transplanted sex glands, with sex-gland extracts (testicular and ovarian) and the observation of infusions of a male-type blood-stream into a female body, as occurs in nature in some cattle and in the so-called human "hermaphrodites," indicate a gross chemical difference between the respective determiners for femaleness and for maleness. So the chemicals involved, though not yet isolated, must be presumed to be qualitatively different, since they produce such different results.
But such experiments also indicate that both determiners must be present in some proportions in every individual of either sex. The basis for both sexes being present, the one which shall predominate or be expressed in the individual must depend upon the quantitative relation between the determiners which come together at fertilization. The quantitative theory merely means that this predominance of one factor or the other (maleness or femaleness—Gynase or Andrase) is more pronounced in some cases than in others.
In brief, then, the quantitative theory of sex is merely the most reasonable explanation of the known fact that intersexes exist—that is, females with some male characteristics, or with all their characters more like the female type than the average, and vice versa. Laboratory biology has established the phenomena of intersexuality beyond question, and the word "inter-sex" has become a scientific term. But the fact that this word and the idea it represents are new to exact science does not mean that it is new in the world.