These facts, and many others that might be quoted, are pertinent to our subject, on account of the influence exercised over the ganglionic centres by the development and functional activity of those of thought. Stimulation of the cerebral hemispheres is one of the most powerful means of counteracting paralysis of the vaso-motor centre, with all its consequences. Habitual activity of these centres--implying, psychologically, habitual activity of thought, physiologically, a more active local circulation--is therefore the best method at our disposal for permanently counteracting tendencies to irregular action in this centre, in the emotional ganglia lying in its vicinity, and in the vaso-motor nerves dependent upon it. A method of such general supervision does not in itself forbid the co-education of girls and boys; for from this more general point of view, the health of the latter during adolescence really requires precisely the same precautions as that of the former. Attention is less frequently drawn to the precautions required in the case of boys, mainly because such precautions are more frequently observed in regard to them. But besides, girls arrive at the period of adolescence already enervated by the senseless training of their childhood, on which distinctions of sex have been obtruded long before they are established by nature. Finally, since peculiarities relating to the sexual organs are inherited, if at all, from the parent of the same sex,[48] the germs of uterine diseases acquired by mothers too frequently exist in daughters, ready to be developed at the earliest opportunity.