The most dangerous symptoms of disease are evidenced in the nervous system. Neurotics are employed to control these symptoms as they arise, but Hæmatics are used to combat the cause of the disorder. As to their relative efficacy, there is an advantage and a disadvantage on each side. On the one hand, nerve-medicines are more numerous and more powerful than blood-medicines, and thus in the control of symptoms they are wielded with more immediate certainty than the others in the counteraction of diseases. On the other hand, the symptom that is dreaded is only relieved for a time by the Neurotic remedy, while the morbid condition that caused it continues, and will perhaps cause it again; but when a disorder is remedied by the employment of Hæmatic medicines, it is more or less permanently cured and put an end to. In the above Proposition I have endeavoured to state as much as we know with certainty of the action of Neurotics. To this certainty I have already ventured to add a surmise, on which no certain reliance can be placed. But even if the theory of the action by atomic shapes should be rejected as improbable, because affording too easy an explanation of a naturally inscrutable operation, it would still seem likely that these medicines may take effect by exerting some minute and imperceptible influence on nerve-fibre, or producing in it some inappreciable disorganization or change, which has the effect of altering the natural performance of its functions. The effect of mechanical concussion or shock, which may produce death by minutely disarranging the particles of the nervous centres, presents an obvious analogy to the sudden and remarkable action of some nerve-poisons. Having offered these vague suggestions as to the ultimate _modus operandi_ of Neurotics, I will now proceed to divide the Proposition in which their more obvious action has been stated into a number of minor propositions. These apply to the whole class. The three divisions will be afterwards shortly considered separately. _m. p. 1._--That Neurotics are medicines which pass into the blood. _m. p. 2._--That their action is evidenced by a change in one or more of those functions which are attributed to the nervous system. _m. p. 3._--That it is necessary that they should pass from the blood to that part of the nervous system which is influenced by them. _m. p. 4._--That they are of use in an over-excited or depressed state of the nervous system. _m. p. 5._--That they are transitory in action, and cannot remain in the blood.