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POPULAR SCIENCE REVIEW. 
effect, by producing which tonics may give strength to the 
system generally. 
Practically it is known of medicines having high tonic powers, 
that they do serve some of these purposes, and of others it is 
fairly surmised. Preparations of iron undoubtedly raise the 
quantity of red blood-globules in the system when this is defi- 
cient, and, these globules being largely concerned in the nutri- 
tion of tissues, ferruginous medicines may thus act as tonics, 
by improving the state of the blood, whatever other tonic 
effects they may cause. The almost certain action of cod- 
liver oil is of a similar kind. It is easily digested and assimi- 
lated, and since every tissue-element has fat-globules, as one 
of its constituents, it must serve nutrition generally, by aiding 
in forming those elements, such as blood- globules, which 
serve nutritive purposes. This oil also, in being derived from 
the liver of an animal, and containing biliary matters, may 
aid in preparing food for assimilation. 
Many substances of value as tonics cause avery bitter taste; in- 
deed, so common is this, that bitterness is generally regarded as 
an indication of tonic powers. In loss of appetite people usually 
resort to ^‘^bitters.^^ Now, ifc can hardly be supposed, as some 
writers seem to imply, that the occurrence of both tonic power 
and bitterness in so many substances is merely an accidental 
coincidence. The taste of a substance is proof of the posses- 
sion by it of certain properties ; and so far as the bitterness of 
different substances is similar, so far must they have properties 
in common. It is not to be admitted that, in causing taste, 
substances are passive ; they must act upon the tongue, and, 
in so doing, undergo some change through expending some of 
their power. Now, the production of a common effect upon 
the tongue by different substances, is a sufficient evidence that 
if they act upon the stomach instead, they may cause a com- 
mon action in it of tonic or other value. For, as we have en- 
deavoured to impress upon our readers, a substance is a tonic 
because it excites certain actions, or stimulates, and therefore 
the power of exciting bitterness may be a proof of the power 
possessed to cause a certain tonic effect. Other and injurious 
properties of a bitter substance may, of course, disqualify it 
for serving as a tonic ; but this does not disprove the proposition 
that bitterness is significant of tonic power. On the other 
hand, bitter tonics, while they may owe some of their tonic 
power to the property by which they excite bitterness, may 
have other properties to give them in part this power. 
