es goitre has been traced to certain mountain springs
in goitrous districts; it has been observed that a patient with goitre
may, through faecal contamination apparently, infect the water supply,
and that conscripts in order to avoid military service have drunk from
goitrous springs with success. Children born in a goitrous district
are liable to be cretins, while if goitrous parents move to a healthy
district, the children are born healthy. If the water supply of a
goitrous valley be changed to a healthy spring, goitre and cretinism
disappear. Thorough boiling of the water rids it of its toxic
properties.

[Illustration: FIG. 277.--Parenchymatous Goitre in a girl aet. 15.

(Mr. D. M. Greig's case.)]

_Morbid Anatomy._--Both the secreting and the fibrous elements share
in the hyperplasia, and the gland as a whole becomes enlarged and
forms a horseshoe-shaped swelling of moderate size in the neck. This
swelling is soft and smooth on the surface, and is seldom quite
symmetrical. In some cases the hypertrophy involves chiefly the
isthmus. In others an outlying accessory lobule of thyreoid tissue
constitutes the bulk of the swelling, and this may extend a
considerable distance from the position of the normal thyreoid,
reaching even behind the sternum into the thorax--_infra-thoracic_ or
_retro-sternal goitre_.

[Illustration: FIG. 278.--Larynx and Trachea surrounded by Goitre.]

[Illustration: FIG. 279.--Section of Goitre shown in Fig. 278, to
illustrate compression of Trachea.]

When the secreting elements increase out of proportion to the stroma,
numerous rounded or irregular spaces filled with a thick yellow
colloid material are formed in the substance of the goitre--_colloid
goitre_. The majority of these spaces are not larger than a pea, but
one or more may enlarge and form cysts of considerable size--_cystic
goitre_. These varieties, especially the cystic form, attain greater
dimensions than any other form of goitre.

When the fibrous stroma is greatly in excess--_fibrous goitre_--the
swelling is smaller, firmer, and shows a greater tendency to contract
and compress the trachea. If the sclerosis is extreme and the
secretory tissue undergoes atrophy, myxoedema may result.

In some cases the hyperplasia affects chiefly the blood vessels of
the thyreoid--_vascular goitre_. The capillaries, veins, and arteries
are increased in size and number; the swelling pulsates and increases
in size when the patient makes an