448 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1919. 
the pineal gland. We have hitherto regarded the pineal gland, little 
bigger than a wheat grain and buried deeply in the brain, as a mere 
useless vestige of a median or parietal eye, derived from some distant 
human ancestor in whom that eye was functional, but on the clinical 
and experimental evidence now rapidly accumulating we must assign 
to it a place in the machinery which controls the growth of the body. 
We come now to deal with the thyroid gland, which, from an an- 
thropological point of view, must be regarded as the most important 
of all the organs or glands of internal secretion. Here, too, in con- 
nection with the thyroid gland, which is situated in the front of the 
neck, where it is so apt to become enlarged and prominent in women, 
J must direct attention to a generalization which I slurred over when 
speaking of the pituitary and suprarenal glands. Each of these 
glands throws into the circulating blood two sets of substances—one 
set to act immediately in tuning the parts of the body which are not 
under the influence of the will to the work they have to do when the 
body is at rest and when it is making an effort; another set of sub- 
stances—which Prof. Gley has named morphogenetic—has not an 
immediate but a remote effect; they regulate the development and 
coordinate the growth of the various parts of the body. Now, so 
far as the immediate function of the thyroid is concerned, our pres- 
ent knowledge points to the gland as the manufactory of a substance 
which, when circulating in the body, regulates the rate of combustion 
of the tissues; when we make a muscular effort, or when our bodies 
are exposed to cold, or when we become the subjects of infection, the 
thyroid is called upon to assist in mobilizing all available tissue fuel. 
If we consider only its immediate function it is clear that the thyroid 
is connected with the selection and survival of human races. When, 
however, we consider its remote or morphogenetic effects on growth, 
its importance as a factor in shaping the characteristics of human 
races becomes even more evident. In districts where the thyroid is 
liable to that form of disease Known as goitre it has been known for 
many a year that children who were affected became cretins—dwarf 
idiots with a very characteristic appearance of face and body.? Dis- 
ease of the thyroid stunts and alters the growth of the body so that 
the subjects of this disorder might well be classed as a separate 
species of humanity. If the thyroid becomes diseased and defective 
after growth of the body is completed, then certain changes, first 
observed by Sir William Gull in 1873, are set up and give rise to the 
disordered state of the body known as myxedema. “In this state,” 
says Sir Malcolm Morris (Brit. Med. Journ., i., p. 1038, 1913), “the 
skin is cold, dry, and rough, seldom or never perspires, and may take 
on a yellowish tint; there is a bright red flush in the malar region. 
2The story of the discovery of the action of the thyroid gland is told by Prof. G. M, 
Murray, Brit. Med. Journ., ii., p. 163, 1913. 
