The New York Board of Health, cites eight different forms in which the disease may appear and acknowledges a startling failure to determine either any uniform period of incubation (i.e. the time between contagion and the appearance of the symptoms,) or the period of infection (i.e. how long a sick person may be a danger to others). The New York press accepts the situation philosophically; as follows: "Infantile Paralysis cannot be cured by means of medicines. The physician must of necessity limit his ministrations to easing the pain, providing for easy movement of the bowels and so forth, but otherwise _he must let nature take its course_." Medical reference books vaguely define the disease with diverse and indefinite theories, showing that science on the subject is practically mute. But the medically "unprofessional," random remark of the New York press-man has exactly hit the mark: "Let nature take its course." The fact is that nothing very clear or absolute can be said about Infantile Paralysis; for observation shows that it is apparently a matter of racial conditions and environment and that only from the general application of the Laws of Nature, as taught by biology can we reasonably hope to solve the problem or cure the disease. As the result of careful study of many cases I simply confirmed the fact that Infantile Paralysis belongs strictly to the class in which in the foregoing chapter I have placed it, and is subject to the same rules, influences and treatment. In most of the cases treated I have not failed to discover the existence of spinal trouble in one or other of the parents. This, engendering _predisposition_ to similar complaints _in the children of the opposite sex_, which, acted upon by the irritants bred of poor or irrational nutriment and unhygienic environment in greater or lesser degree, results in attacks of this disease, in plain or epidemic form as the case may be, to which all children so predisposed are liable. Thus, incidentally, is my recently discovered "Law of the Cross-Transmission of Characteristics" amply verified.