THE FUNCTION OF TANNIN. 
269 
SOME INVESTIGATIONS INTO THE FUNCTION OF 
TANNIN IN THE VEGETABLE KINGDOM. 
BY W. HILLHOUSE, M.A., F.L.S. (PRESIDENT).* 
In working, during the winter of 1882-3, upon the question 
of the movements of food-substances in the plant during the 
period when the chlorophyll-function is not being carried 
on, I was much impressed by the wide distribution and often 
abundant presence of that variable body known generically as 
tannin. It seemed to me to be hardly credible that a body 
so prevalent in vegetable growth should have no direct 
relations of utility to the plant. My attention being thus 
directed to the matter, I endeavoured during the ensuing 
summer to carry on, in the intervals of other work, a few 
investigations into the relations of tannin with plant life, 
which are here recorded, the temporary loss of the manuscript 
through a domestic removal being almost wholly responsible 
for the delay in publication. 
In the large series of bodies, which, from their capability 
of resolution by boiling with dilute acids or alkalies, or by 
the action upon them of ferments, into a glucose and one 
or more other compounds, are grouped together under the 
generic name of Glucosides, there is none which approaches, 
whether in economic importance, universality of distribu¬ 
tion, or physiological interest, to the group of the tannins, 
or, as I shall hereafter as a rule speak of them, to tannin. 
General Chemistry.— In all its forms tannin is charac¬ 
terised by a weak acid reaction, and an easily recognisable 
astringent taste. As obtained, it forms a shining amorphous 
powdery mass, freely soluble in water and alcohol, producing 
characteristic reactions with ferric salts, precipitating a solution 
of gelatine or albumin, and uniting with animal membrane 
so as to produce a substance (leather) which is capable of 
resisting decomposition. This latter property is the scientific 
basis of the process of tanning. 
Although we shall find it convenient hereafter to speak of 
the group under a single name, it must be borne in mind 
that the name includes a considerable series of bodies, of 
slightly varying character, and our knowledge of which is 
still extremely limited. Most of them appear to be gluco¬ 
sides of gallic acid, and capable of resolution into gallic acid 
_ - _____ 
* Transactions of the Birmingham Natural History and Micro¬ 
scopical Society, Biological Section, June 14th, 1887. 
