444 
POPULAE SCIENCE EEVIEW. 
Let us now consider tonics and stimulants together. To 
stimulate and to give tone^ are not only very different actions, 
but actions essentially opposed in nature. For to give tone is 
to give strength and power, while, as formerly remarked, to 
cause the body to do anything, is to cause it to expend some 
of its power. This must be the case by the law of conser- 
vation of force, which is that force can neither be created nor 
annihilated by any natural occurrence ; and it is also proved 
to be so by chemico-physiological researches. Since, then, 
these two actions are opposite in nature, our readers may feel 
surprised to learn that we are now going to show that, so far 
from tonic agents being necessarily opposed in their effects to 
stimulants, the former are such through possessing stimulant 
properties, — that, in fine, tonics are stimulants. It is easy 
enough, however, to show this to be so, for it is only paradoxi- 
cal in appearance. To give strength to the system by causing, 
or assisting to cause, nutriment to be taken up by it,- — the 
property of a tonic, — can only be done by exciting various 
vital actions of the system, by which it prepares and assimi- 
lates this nutriment ; for, of course, we exclude the effects of 
substances upon each other in the stomach, by which they may 
be rendered more digestible, as independent of the system, 
and therefore, in no sense, vital or physiological effects. Thus 
viewed, then, it becomes evident, that to act as a tonic is so 
to stimulate the system, as that it manifests such of its powers 
as serve to assimilate those matters fitted for nutritive purposes. 
Hence our assertion, that a tonic is a stimulant, is correct. 
There follows from what we have said, that a tonic, in acting 
as a stimulant, causes an expenditure of bodily power, while 
that by serving to aid the process of assimilation of nutrient 
matters by the organism, it causes an additio7i of bodily power. 
A little consideration, therefore, will be sufficient to convince 
any one that for a substance to be of use as a tonic, it 
must act in such a way as to cause the body to receive more 
power in the shape of substance added to its structures, than 
it has to expend in the actions which the medicine calls forth 
in it, by which digestion and nutrition are advanced. Physio- 
logy shows that good food when digested and assimilated 
affords to the system much more power in its own substance 
than it causes to be spent in making it a part of the organism, 
in preparing gastric juice and other secretions to act upon it, 
in working and kneading it m the stomach, and in other 
processes. And it must be, for a medicine to act as a tonic 
that it only calls forth those actions aiding assimilation of food 
to the extent necessary for that purpose. For if it proceeds 
further than this, it wastes the powers of the body — expends 
them to no purpose, — and is further liable to cause harm, in 
