If it is, perhaps, somewhat excessive to declare, with Johnstone, that "woman is the only animal in which rut is omnipresent," we must admit that the two groups of phenomena merge into or replace each other, that their object is identical, that they involve similar psychic conditions. Here, also, we see a striking example of the way in which women preserve a primitive phenomenon which earlier in the zoölogical series was common to both sexes, but which man has now lost. Heat and menstruation, with whatever difference of detail, are practically the same phenomenon. We cannot understand menstruation unless we bear this in mind. On the psychic side the chief normal and primitive characteristic of the menstrual state is the more predominant presence of the sexual impulse. There are other mental and emotional signs of irritability and instability which tend to slightly impair complete mental integrity, and to render, in some unbalanced individuals explosions of anger or depression, in rarer cases crime, more common;[107] but the heightening of the sexual impulse, languor, shyness, and caprice are the more human manifestations of an emotional state which in some of the lower female animals during heat may produce a state of fury. The actual period of the menstrual flow, at all events the first two or three days, does not, among European women, usually appear to show any heightening of sexual emotion.[108] This heightening occurs usually a few days before, and especially during, the latter part of the flow, and immediately after it ceases.[109] I have, however, convinced myself by inquiry that this absence of sexual feeling during the height of the flow is, in large part, apparent only. No doubt, the onset of the flow, often producing a general depression of vitality, may tend directly to depress the emotions, which are heightened by the general emotional state and local congestion of the days immediately preceding; but among some women, at all events, who are normal and in good health, I find that the period of menstruation itself is covered by the period of the climax of sexual feeling. Thus, a married lady writes: "My feelings are always very strong, not only just before and after, but during the period; very unfortunately, as, of course, they cannot then be gratified"; while a refined girl of 19, living a chaste life, without either coitus or masturbation, which she has never practiced, habitually feels very strong sexual excitement about the time of menstruation, and more especially during the period; this desire torments her life, prevents her from sleeping at these times, and she looks upon it as a kind of illness.[110] I could quote many other similar and equally emphatic statements, and the fact that so cardinal a relationship of the sexual life of women should be ignored or denied by most writers on this matter, is a curious proof of the prevailing ignorance.[111]