REPORT OF MEDICAL SECTION. 145 
different textures, such as skin, muscle, cellular membrane, and 
adipose substance ; yet as it can hardly be supposed that they 
are all equally prone to it, it seems probable that its having 
commenced in one tissue tends to determine its taking place in 
others in contact with it. 
As a connecting link between changes resembling those just 
adduced, and those which occur in living organized bodies, may 
be mentioned the well-known fact, that many fruits gathered 
long before their living connection with the root would have 
naturally ceased, notwithstanding undergo those changes which 
render them ripe, or in other words, bring them to a state of 
maturity. In the leaves of plants, a short time before they lose 
their connection with the branch, and also when they have been 
detached from it, a chemical change takes place, which produces 
the Xanthophylle or yellowcolouring principle on which the hues 
of autumn in great measure depend. Before we can apply the 
principle of these changes to the assistance of our investigation 
of the changes effected in living bodies, it is important that the 
laws which regulate them should be further elucidated. The 
labours of some of our continental chemical brethren have already 
considerably advanced the subject. Without swelling this pre- 
liminary report with an analysis of what they have done, it will 
be sufficient for our present purpose to adduce, without attempt- 
ing any chemical explanation, some of the apparently parallel 
phenomena to which we invite the attention of those who may 
be disposed to co-operate in this kind of research. As farina 
or starch may be converted into gum, and both farina and gum 
into sugar, and these into various acids, or into alcohol or ether, 
so it would appear that other principles may be changed ac~- 
cording to a particular course of succession, though some of the 
possible links may not be always essential.. The very possibi- 
lity of such successive changes renders it necessary to take into 
consideration another element, viz., time; and in our inquiry 
into the production of different secretions, we must, besides in- 
vestigating the anatomical and chemical composition of the 
secreting organ, and the qualities of the matter when first pro- 
duced, as compared with its ultimate state, not fail to take ¢éme 
into the consideration. The first rapidly produced. secretion 
from a mucous surface is: nearly serous. Newly and rapidly 
formed mucus is thin and aqueous. when compared with that 
which has been long detained upon the surface of the secreting 
membrane. When milk is too frequently drawn. from the lac- 
_ tiferous glands it is thin and watery compared with that which 
is allowed to be longer retained. The production of pus is 
another example, and one in which the changes may be followed. 
VOL. VI. 1837. L 
