Our knowledge of the normal metabolism of the body is very imperfect, consequently we know very little more than has already been stated under other divisions, about the action of drugs on metabolism. Any further remarks which are necessary will be made when the individual drugs are considered. Two words in common use are alterative and tonic.

Alterative is a vague term of which no definition can be given. It is often used to cloak our ignorance, when we have no exact knowledge of the action of a drug. Many drugs comprehended under this term have the property of profoundly altering the body, especially if it be diseased; for example, mercury will, if the patient be suffering from syphilis, generally cause the absorption of syphilitic exudations, but we do not know how this takes place. All that can be said about such drugs will be stated under each, for their mode of action is probably so different that no useful purpose would be served by considering them together.

Tonic

This is a term even more vague than alterative. So ill-defined is it that it is advisable never to use it if it can be avoided. As commonly employed, it means a drug which makes the patient feel in more robust health than he did before he took it. Obviously this may happen in many ways, such as, for instance, by improving the digestion or the quality of the blood. This definition is evidently inadequate, and none thus far proposed is entirely satisfactory. The following is suggested (Wood): A drug which so influences nutrition as to increase the reconstruction or upbuilding of the tissue or tissues concerned.