On the occurrence of the œstrous cycle after X-ray sterilisation.—Part I. Irradiation of mice at three weeks old

The cyclic activities of the female reproductive organs of mammals, constituting the œstrous cycle, fall naturally into two main series,i. e ., the uterine cycle and the ovarian cycle, and the correlation between these two forms one of the most intricate problems of internal secretion. Two chief problems are presented—(a ) what stimuli produce the uterine cycle in the first place, and (b ) how is the uterine cycle so synchronised with the ovarian cycle as to result in the uterus being ready to receive the fertilised ovum just after the time of ovulation? Since ovariotomy results in cessation of the cycle, whereas excision of the other reproductive organs has not this effect, it is necessary to suppose that the controlling power resides in the ovary, and further, since transplantation of the ovary does not result in the cessation of the cycle, that the means of control is hormonic. The alternating maturation of follicles andcorpora lutea in the ovaries is exactly synchronised with the changes which take place in the uterus, and it is therefore reasonable to look to the periodic growth of one or other of these ovarian structures for the origin of the periodic hypertrophy of the uterus. Owing to the fact, however, that in many mammals œstrus sets in when nocorpora lutea are present in the ovary, these structures can be eliminated as originators of the œstrous cycle. Similarly, the supposition that the corpusCorpus luteum has an inhibitory effect, the removal of which allows œstrus to appear, can only be applied to certain special conditions. If, therefore, any cyclic structure of the ovary is responsible for the regulation of the œstrous cycle, it must be the maturing follicle. This conclusion is supported by the following facts:— (a ) Œstrus first appears when ovulation starts at puberty, and the œstrous cycle stops when ovulation ceases at the menopause.