In an investigation of the incidence of the sex chromatin of intermitotic nuclei in the various tissues (skin, stomach and muscle) of 37 human embryos (crown-rump length 7.9-318mm) and the ventral abdominal skin of 20 patients (10-80 years old), the following results were established.
1. In the early stages of 7.9-35.6mm crown-rump length (4-9 weeks), the sex can not be determined from the form of external genitals, without error, but it is possible to distinguish it from the incidence of the sex chromatin of intermitotic nuclei.
In the female embryos, the sex chromatin was identified in a comparatively high percentage of nuclei, and there are no marked differences of these percentages between the various tissues, as follows.
In the epidermis of skin: adj. (adjacent to nuclear membrane) 55.9%, free (free from nuclear membrane) 35.4%:
In the derma of skin: adj. 61.1%, free 18.6%.
In the gastric epithelium: adj. 55.5%.
In the gastric submucosa: adj. 57.1%.
In the striated muscle (premuscular cell): adj. 65.3%.
In the cardiac muscle (premuscular cell): 60.0%.
In the smooth muscle (premuscular cell): adj. 64.8%.
In the male embryos, the sex chromatin was identified in a comparatively low percentage of nuclei in each case, averaging 2.8% (0-7.6%).
2. The changes of incidence of the sex chromatin adjacent to the nuclear membrane with development are classified into the following three types.
Type 1. The incidence of sex chromatin scarcely changes during the prenatal and postnatal stages and is constantly about 50%, as seen in the epidermis of skin (cf. Fig. 1).
Type 2. The incidence of sex chromatin falls into a low percentage (to about 30%) at the middle of the fetal stage but afterward it does not change until the last stage, as seen in the gastric epithelium (cf. Fig. 2).
Type 3. The incidence of sex chromatin is about 50% at the middle of the fetal stage. Afterward, at the about 250mm stage (of 29-30 weeks) it falls into 30% or to a much lower percentage and then it does not change until the last stage, as seen in muscles (cf. Fig. 3).
3. In the germinal layer of skin in female embryos, the incidence of the sex chromatin free from the nuclear membrane is about 38.6% at the primary fetal stage, but afterward in the time of the middle or the last fetal sfage, it falls into a remarkably lower percentage (to 10.2-19.4%).
In the infant and adult stages, the incidence changes from 4.6% to 27.6%, but it has no correlation with the age factor. The incidence of this type gives some additional increases or decreases with the incidence of the sex chromatin adjacent to the nuclear membrane and so the particularly low samples of the incidence can not be found in the average (cf. Fig. 1).
4. It seems that, in each tissue, the period of declining of the incidence of sex chromatin has a correlation with that of the functional differentiation.
5. In the male, the incidence of sex chromatin is always in low percentage, and so it is possible to distinguish the sexual dimorphism from the incidence of sex chromatin. However, in the derma of skin and the gastric submucosa in the last fetal stage it becomes very difficult to distinguish the sexual dimorphism, because the incidence of sex chromatin in the female falls into a low percentage like the male (cf. Fig. 1).
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