Experience proves the potent character of mental stimuli in moulding practical action. Fear or hope, curiosity, vanity, cupidity, when regardless of the Law of Unity, seize upon isolated phenomena removed from their natural connection, and distort them by creating morbid conditions, thus viewing facts out of proportion. Statistics thus formed become fallacious, and serve as the bases of dangerous theories--theories which, unless checked by popular common-sense from being put into practice, would cause the moral and physical degradation of the race. I need only refer to the folly of injustice embodied in certain medical acts lately abolished and to the present theory of inoculation, as noteworthy instances of dangerous mental delusion desiring to shape itself into action. Materialism, which is blind to other than sensuous life, which insists upon reducing every phenomenon to the limits of the senses, which refuses to be enlightened by any higher reality, or sneers at the term ‘vitality,’ neglects a great range of positive facts, and has no right to the noble name of science. Reflection, therefore, shows that the moulding and guiding power of mental action in shaping physical results being a fact of the most far-reaching character and of permanent operation in sentient creation, its omission in a Congress of Health was a serious injury to the results of the Congress. It was a sufficient reason for that sterility of result which has been publicly and privately expressed. The error of not recognising mental as well as physical forces, or the Law of Unity, in relation to health, and the tyranny that may result from such imperfect method in the study and application of sanitation and medicine, may be illustrated by an interesting incident of the Congress. An important joint meeting of two sections took place in order to listen to the discourse of one of our ablest investigators--a man in high position, and one who wields a powerful influence on the rising generation of medical students. This gentleman early in his discourse made the following noteworthy announcement: ‘I claim the right of science to dictate’--and as if to strengthen this claim by the authority of our French brethren he added ‘conformément à la logique’--‘I claim the right of science to dictate in accordance with logic.’