1. In the higher animals control of the functions of the body is dual, being partly neural and partly humoral.
2. When the control of any function is single and not dual, it is entirely neural. Exceptions to this statement appear to occur in connexion with the secretion of urine and milk, since these functions have not hitherto been shown to be under direct neural control. The mamma, and perhaps the kidney also, is, however, influenced by certain internal secretions which are themselves subJect both to neural and to humoral control.
3. The functions which are controlled both neurally and humorally are initiated by direct nervous influence: the humoral influence succeeds this.
4. In the lowest organisms possessed of a nervous system there is no evidence of humoral control, and no probability that this could be exercised, since there is no circulatory fluid, and the fluid which bathes the tissue has a composition appreciably the same as that of the environment.
5. It is, therefore, inferred that in all cases in which a dual control exists the neural, which is more rapid in its action, is primary, and the humoral secondary; and that the object of the humoral influence is to continue and prolong the effect of the neural influence, and thus to effect an economy of nervous energy.