The _Tenth Proposition_ treats of Eliminatives. It is not said simply that these increase the secretions of a gland; or that they stimulate the glands while passing by them in the blood. But it is laid down as a rule that they act by themselves passing out of the blood through the glands, and that while so doing they excite them to the performance of their natural function. They are substances which are unnatural to the blood, and must therefore pass out of it. In so doing they tend to pass by some glands rather than by others: in these secretions they may be detected chemically; and it is on these glands that they have an especial influence. Their uses in treatment are various and manifold. In these classes are included all medicines that act after entry into the blood. On referring to the classification which precedes this chapter, it will be seen at a glance what groups of medicines are arranged as orders under each class or division.[6] In the third chapter I shall attempt at some length to prove the propositions which treat of these four classes; and I shall also attempt to explain the nature and mode of action of the orders, or small groups of remedies. In the fourth chapter some of the more important medicines will be considered separately, either as individually interesting, or as illustrative of general modes of operation previously described. I may point to some parts of the Essay as being more original than others, although not perhaps for that reason more valuable. For this purpose may be mentioned the treatment of the second proposition: the distinction attempted to be drawn between the two divisions of blood-medicines; the account given of Tonics in one of these divisions, and of Anti-arthritics in the other; the theory of the action of Eliminative medicines; and the experiments made on the action of Aconitina. CHAPTER II. ON SOME OF THE MORE IMPORTANT CLASSIFICATIONS OF MEDICINES, AND OPINIONS OF AUTHORS RESPECTING THEIR ACTIONS. I have thought it necessary, before stating at length my own conclusions, to refer to some of the more important statements of authors concerning the subject of which I have to treat; because by so doing I may to some extent indicate what points are to be regarded as determined and proved, and what as still unsettled, and point out where I can agree with other writers, and where I am disposed to differ from them. The opinions of authors on the general action of medicines are in most cases best ascertained by observing the manner in which they have arranged and classified them, grouping together those which they consider to be alike in their mode of operation.