In another way this biological factor makes itself felt, and that is in the differences in the muscular systems of men and women. These we must also consider fundamental. Although the extreme muscular weakness of average civilised women as compared to civilised men is certainly artificial and easily possible to remove by training, yet even in savages, among whom the women do most of the muscular work, they seldom equal or exceed the men in strength; any superiority, when it exists, being mainly shown in such passive forms of exertion as bearing burdens. In civilisation, even under the influence of careful athletic training, women are unable to compete muscularly with men; and it is a significant fact that on the variety stage there are very few "strong women." It would seem that the difficulty in developing great muscular strength in women is connected with the special adaptation of woman's form and organisation to the maternal function. But whatever the cause may be, the resulting difference is one which has a very real bearing on the mental distinctions of men and women. It is well ascertained that what we call "mental" fatigue expresses itself physiologically in the same bodily manifestation as muscular fatigue. The avocations which we commonly consider mental are at the same time muscular; and even the sensory organs, like the eye, are largely muscular. It is commonly found in various great business departments where men and women may be said to work more or less side by side that the work of women is less valuable, largely because they are not able to bear additional strain; under pressure of extra work they give in before men do. It is noteworthy that the claims for sick benefit made by women under the National Insurance System in England have proved much greater (even three times greater) than the actuaries anticipated beforehand; while the Sick Insurance Societies of Germany, France, Austria, and Switzerland also report that women are ill oftener and for longer periods than men. Largely, no doubt, that is due to the special strain and the rigid monotony of our modern industrial system, but not entirely. Nearly two hundred years ago (in 1729) Swift wrote of women to Bolingbroke: "I protest I never knew a very deserving person of that sex who had not too much reason to complain of ill-health." The regulations of the world have been mainly made by men on the instinctive basis of their own needs, and until women have a large part in making them on the basis of their needs, women are not likely to be so healthy as men. This by no means necessarily implies any mental inferiority; it is much more the result of muscular inferiority. Even in the arts muscular qualities count for much and are often essential, since a solid muscular system is needed even for very delicate actions; the arts of design demand muscular qualities; to play the violin is a muscular strain, and only a robust woman can become a famous singer.