There has always been greater difficulty in furnishing legal protection against the risk of disease in industrial employment than against the risk of accident. The common-law liability of the employer for illness contracted by the employe in consequence of defective arrangements may be regarded as a negligible factor, owing to the difficulty of legally proving the cause of disease and to the operation of the doctrine of assumption of risk. It is only since 1906 that a statutory liability for disease has, within a very narrow range, been established in England, and such a thing is not even agitated in this country. For protection against occupational disease and its consequences our laws rely upon preventive regulation entirely. No system of protective devices, however, can banish altogether the baneful effect of certain occupations upon the general health and strength of the worker, and it is against these inevitable risks that reliance must be placed upon diminishing the amount of exposure, _i. e._, reducing the hours of labor. This reduction is, of course, also the only remedy against the specific evil effects upon the human system of overexertion and fatigue. A demand which has generally been understood to serve economic or social purposes may thus assume the character of a sanitary requirement, and the confusion of purposes is aggravated by the fact that of all sanitary risks that of a mere prolongation of effort under undesirable conditions is the least tangible, as well as the most variable according to individual constitutions, and that the legal maximum of duration of work must be more or less haphazard and arbitrary. The resulting difficulty in the application of constitutional principles is obvious. If the courts are expected to protect the freedom of contract, as the legislature is expected to protect the public welfare, can the mere enactment of a statute be accepted as conclusive as to the requirements of the public health and safety? Up to the present time the courts have not succeeded in evolving any definite theory with reference to this problem; it is a matter of speculation whether in a given case they will acquiesce in the legislative judgment or override it.