126 Proceedings of the Royal Physical Society. 
indicate the light which these investigations throw upon 
biological processes, giving us glimpses of the elaborate 
and subtle conditions which influence and determine our 
physical and even our mental constitution. 
I cannot do this without going into some questions which 
are to some of you an oft-told tale, but they cannot be 
known to all of you; so those who know must bear for the 
sake of those who know not. 
The first discovery to which I shall refer is the best 
known of many to which reference will have to be made. 
There is in man and the higher animals a gland in the neck 
which is known to anatomists and others as the Thyroid 
Gland. It belongs to the class of glands which are without 
a duct by which to discharge their special secretion. The 
function of this gland was unknown until quite recently; 
not only so, but it was questioned whether it performed any 
special function or useful purpose whatever in the animal 
economy. I have, indeed, a recollection that, in my student 
days, when the argument for design was advanced, and 
illustrated from the human body, the Thyroid Gland was a 
stumbling-block, for there was either an idea, or an accepted 
conviction, that this gland had been left by mistake; that 
it was one of those organs, stranded on the shores of the 
stream of evolution, having the same kind of interest as the 
finding of a Norse galley on the shore of Labrador would 
have; the one revealing the evolutionary antecedents of man, 
the other revealing an America known before Columbus. 
This was the state of ignorance within the last twenty 
years, and our present knowledge is mainly the outcome of 
investigations suggested by a series of observations in cases 
in which the gland had been removed for surgical reasons, 
and having no connection whatever with a desire to become 
acquainted with its function. The discovery might in this 
respect be looked upon as accidental, or, at all events, 
merely incidental. It is not my purpose to trace the steps 
by which our knowledge has been attained, so I may at once 
proceed to the facts which have been correlated, and the 
light they have thrown upon a hitherto dark region. Some 
of you are doubtless aware that in certain districts of 
