SYNTHETIC WORK IN CARBOHYDRATES 327 
anti-tartaric acid. This is the result of synthesis, and is not 
decomposable into active parts. 
A nti-tartaric A cid. 
COOH 
OH-H 
OH-H 
COOH 
From what has been said it will be easy to understand the 
parallelism of Pasteur’s classical experiments with the sugars 
and the application of this theory to other classes of com¬ 
pounds. 
With the simple sugar molecules the conditions are not so 
complex as in the higher sugar series, and the number of Stereo¬ 
mers is less. With an increasing number of carbon atoms the 
conditions of asymmetry increase and stereomers are more 
numerous. 
In the case of glucose the number of asymmetrical carbons 
is four. The possible number of stereomers is sixteen, of which 
eleven are known. Among these, five are optical pairs. That 
is, each member of these optical pairs turns the plane of polar¬ 
ized light in an opposite direction, and one of the pair may 
be described as the reflected or “mirror image” of the other. 
When it is remembered that glucose refers to a compound 
which appears under two forms in respect of its action on 
polarized light, the explanation, from what has gone before, 
of this quality is seen to rest on the space position of its atoms. 
The position of the hydrogen and hydroxyl groups, with re¬ 
spect to the asymmetrical carbons in the molecule of the ac¬ 
tive glucose, which turns the plane of polarized light to the 
right, is diametrically opposite to the position in space of these 
same atoms and groups in the other modification of glucose, 
which turns the plane of polarized light to the left. 1 
The right glucose may be spoken of as the “mirror image” 
1 This was represented on a diagram. 
