THE CAUSATION OF DISEASE. 5 3 



to pass spontaneously through rhythmical changes, by being 

 repeatedly subjected to a rhythmically recurring E. 



Are there any rhythmical changes in man answering to the 

 rhythmical movements of the moon round the earth ? It is 

 difficult to say. I have heard people wonder at the curious 

 fact that the ordinary menstrual rhythm coincides,- as regards 

 the length of the rhythm, with the monthly lunar cycle. If, 

 however, the two were in any way causally related, one would 

 expect menstruation to recur at the same time in every woman, 

 but it does not. In one passage, Darwin vaguely alludes to 

 the influence of the lunar rhythm on man. He points out that 

 it distinctly influences many aquatic animals through its in- 

 fluences upon the tides, and he obscurely hints that man may 

 have faintly inherited the rhythmical impress from some far off 

 aquatic ancestor. 



When a rhythm is once established it tends to go on inde- 

 finitely ; one would therefore marvel that the menstrual rhythm 

 should cease, as it is supposed to do, during pregnancy and at 

 the menopause. Probably, however, this does not occur. 

 Throughout the whole of pregnancy the monthly rhythm goes 

 on. I have satisfied myself that this is so from observation,* 

 though there is probably no ripening of an ovum, nor is there 

 loss of blood, unless it be exceptionally. It is recognized that 

 the uterus undergoes muscular contraction throughout the whole 

 term of gestation (indeed, such rhythmic contractions have 

 been regarded as an absolute sign of pregnancy), but they 

 are palpably increased at the time when the period would 

 have occurred, were the woman not pregnant. These monthly 

 contractions are related to the ordinary menstrual contractions, 

 for at the menstrual epochs the uterus undergoes considerable 

 muscular contraction ; and it is to the latter, I take it, that the 

 pain of menstruation is chiefly due. At all events, Dr. J. Mat- 

 thews Duncan, probably the greatest authority on the subject, 

 teaches that the chief form of dysmenorrhea is spasmodic ; the 



* Laycock maintained that the menstrual change took place during preg- 

 nancy. He observes, "it is singular that this doctrine maintained by the 

 ancients should have fallen into neglect. Aetius expressly states, • circa con- 

 sueta purgationis menstruae tempora aggravantur prsegnantes et mamma intu- 

 mescunt lumbi difficulter moventur, vesica rubens et ignitum lotium excernit.' " 

 — Laycock, Nervous Diseases of Women, p. 46. 



