WHAT IS A TONIC ? 
445 
consequence of tlie actions it lias developed falling upon mat- 
ters in and composing the body, so as to unfit them for their 
purposes. It is well known to the physician, for instance, that 
tonics employed in full health, or otherwise inappropriately, 
are not only of no service as such, but frequently cause both 
exhaustion and irritation, exhibited in feelings of discomfort 
and distressing excitement. 
The fact of the manifestation of the effects of tonics being 
almost insensible, has been made the grounds for denial by 
some that they are stimulants at all, although small doses 
of some stimulants are admitted to be tonics. But if, 
as we have set forth, medicines acting as tonics do so 
by stimulating any of the processes of nutrition, the actions 
they thus excite must naturally be almost insensible, and if 
they do not stimulate the body to actions of value to nutrition, 
how do they improve the tone and texture of organs ? Such 
a character of tonic stimulation may indeed serve to dis- 
tinguish it from other forms of stimulation ; but then this is 
implicitly included in that we have given, namely, that tonic 
stimulation is the aiding assimilation and nutrition, by excit- 
ing certain actions. Some substances, like wine in moderate 
doses, may, in appropriate cases, produce both tonic and other 
stimulation, — aid nutrition, that is, and cause sensations often 
grateful by other actions which they excite. 
We have now stated the nature of the effects of tonics and 
their relations to nutrients and stimulants : we trust our reply 
to What is a Tonic ? is satisfactory to the minds of our 
readers. In summary form it is this : A tonic is a substance 
giving vigour to a debilitated system through causing a more 
healthy condition of its structures, — not by supplying material 
for these structures, but by exciting actions in it conducing to 
a more perfect assimilation of material by it. 
Yv^e can say very little of what are the actions which tonics 
excite, beyond this, that they must be some of those which are 
exhibited during the ordinary nutrition of a healthy organism. 
During digestion food is submitted to various fluids, — saliva, 
gastric juice, bile, gpancreatic juice, and intestinal juices, — which 
serve to act chemically upon it : to act upon these fluids, or 
rather their sources, so as to render them more fitted for pro- 
ducing the requisite changes in it, and to cause them to be 
produced just in the quantities most useful, must be important 
actions of tonics. To render the blood more suitable for taking 
up digested food, acting on it, and yielding it up in due form 
and quantity to the tissues must be another action. An increased 
degree of organisation of the structure of the alimentary canal, 
itself a result of tonic infiuence, must also be an important 
