86 STUDIES ON APPLES. 
COMMENTS ON THE PROBLEMS INVOLVED. 
From the foregoing review pectin bodies would be defined as sub- 
stances of undetermined function, very widely distributed in plant tis- 
sues. Pectin bodies occur both in the juice and mare, i. e., in soluble and 
insoluble forms. The latter form, according to the work of Scheibler, 
Wohl, Van Niessen, and others, and from the work done in the Bureau 
of Chemistry, seems to be resolved into soluble forms by boiling with 
water. The solutions possess considerable viscosity, the property of 
forming jellies with precipitants—such as alcohol, sugars, solutions of 
salts, and pectase—and usually rotate polarized light to the right. 
The rotating power of the different pectin bodies appears to vary con- 
siderably. The distinctions laid down by Frémy as existing between 
the pectin bodies seem to be based on uncertain physical properties “@ 
and on the amount of lead with which they will combine. Criteria 
adopted by later workers are based mainly on chemical behavior and 
action on polarized light. - 
Chemically, pectin bodies are characterized by yielding reducing 
sugars, furfurol, and mucic acid in widely varying amounts, according 
to the source of the pectins and the method employed in isolating 
them. These variations may be largely due to varying degrees of 
hydration and to impurities in the pectin bodies examined.  Dif- 
ferences in the pectin bodies themselves, however, are indicated 
by the results of Ullik and Herzfeld. Pectins are profoundly 
changed by alkalis with the formation of salts of the so-called 
pectic acid, the free acid being insoluble in water. Acid groups 
appear to be formed even by treatment with very dilute alkali fora 
very short time, so that extraction with alkali of pectins from plants 
does not recommend itself to the writers when a study of the dissolved 
material is desired. 
The most important problem appears to be the quantitative deter- 
mination of the pectin bodies occurring in a given tissue, because 
such a method could be used to determine the function of the material 
in plants—whether, for example, it is a reserve material, a by-product, 
is used for structural purposes, or has all three functions or two of 
them; whether the nature of the pectin body changes with the 
growth or age of the tissue, or possesses a practically constant com- 
position; whether the pectin bodies obtained from different sources 
are identical, are mixtures of the same substances (such as araban and 
galactan) in varying proportions, or are inherently different. 
It is of interest to note that all pectin bodies thus far studied have 
been derived from the softer tissues. The harder woody material has 
not been considered. 
aj. prak. Chem., 1884, 30: 370. Neue Ztg. Zucker-Ind., 1885, 14: 151. 
