At present, however, this is extremely difficult to do at all satisfactorily, and quite impossible, indeed, to do in a manner likely to yield absolutely unimpeachable results. Nevertheless, a few series of observations have been made. Thus, Dr. Harry Campbell[165] records the result of an investigation, carried on in his hospital practice, of 52 married women of the poorer class; they were not patients, but ordinary, healthy working-class women, and the inquiry was not made directly, but of the husbands, who were patients. Sexual instinct was said to be present in 12 cases before marriage, and absent in 40; in 13 of the 40 it never appeared at all; so that it altogether appeared in 39, or in the ratio of something over 75 per cent. Among the 12 in whom it existed before marriage it was said to have appeared in most with puberty; in 3, however, a few years before puberty, and in 2 a few years later. In 2 of those in whom it appeared before puberty, menstruation began late; in the third it rose almost to nymphomania on the day preceding the first menstruation. In nearly all the cases desire was said to be stronger in the husband than in the wife; when it was stronger in the wife, the husband was exceptionally indifferent. Of the 13 in whom desire was absent after marriage, 5 had been married for a period under two years, and Campbell remarks that it would be wrong to conclude that it would never develop in these cases, for in this group of cases the appearance of sexual instinct was sometimes a matter of days, sometimes of years, after the date of marriage. In two-thirds of the cases there was a diminution of desire, usually gradual, at the climacteric; in the remaining third there was either no change or exaltation of desire. The most important general result, Campbell concludes, is that "the sexual instinct is very much less intense in woman than in man," and to this he elsewhere adds a corollary that "the sexual instinct in the civilized woman is, I believe, tending to atrophy."