THE DUCTLESS GLANDS 323 
disappearance of the dyspnoea was observed. However, 
a similar attempt upon another hyena and a wolf failed 
possibly because no large thin-walled cyst was present. 
These and the case of the lion cub (page 170) are the 
only instances in which the enlarged thyroid seemed to 
have given serious difficulty, and the symptoms were 
probably due to pressure. Many, indeed most, enlarged 
thyroids have been found at autopsy, when the Garden 
personnel was unaware of their existence. Interesting 
notes of familial cretinism will be found under the 
appropriate heading. 
Pathological Anatomy. Classification. 
And now to return to the question of morbid anatomy 
of the thyroid gland, I shall begin by outlining briefly the 
classification to be used in analyzing our cases, a system 
which combines those of many pathologists, yet which I 
believe contains the essentials of all. The changes in the 
gland being hj^Derplastic and recessive, at times to a stage 
of atrophy, no clear cut definite line of demarcation 
separates all these pictures ; instead they must be thought 
of as merging into one another. When the thyroid 
enlarges more or less continuously with a maintenance 
of considerable colloid, the picture is that of colloid 
GOITRE. The gland is pale, gelatinous, tense but resilient 
and may show large cystic areas with fluid contents. 
Microscopically studied the acini are overfilled with col- 
loid yet the lining cells are retained but flattened. The 
cysts may show the ruptured septa of the original acini. 
Enlarged soft reddish glands are found at times to con- 
tain much colloid, nearly every acinus being distended 
with it, but in such organs the epithelia are high or even 
reduplicated; the amount of contents is the striking 
feature. These are termed hyperplasia with colloid. 
'Hyperplasia may go on with the absorption of colloid, 
hyperplasia without colloid. The gland is then a darker 
body of more solid character, red, dull purple or uni- 
