THE DUCTLESS GLANDS 325 
aciiii are compressed, the cells vacuolated or crushed out 
of existence or there may be colloid cysts. 
Inflammations occur as swellings of the interstitial 
tissues and of the acinus cells during many acute infec- 
tions. Repetitions of this may leave a definite increase 
of connective tissue with large cells in the acini, a lesion 
which many observers have looked upon as underlying 
certain goitres and myxedema. 
Hyperplasias. 
The cause of progressive hyperplasias has been 
ascribed to infection, to chemical substances in water and 
food, endogenous toxins, heredity and many other fac- 
tors. While we can add nothing definite in this matter it 
is worthy of notice that all our animals are exposed to the 
same general climatic conditions, receive the same water, 
are fed from the same stocks and many varieties may be 
in charge of the same keeper. The influence of preexisting 
infections cannot of course be measured. Inbreeding or 
captive breeding seems to have a very definite effect upon 
thyroid insufficiency as is well known and so shai'ply 
emphasized by McCarrison in his reference to intermar- 
riage among certain Moslems ; I shall cite the history of 
a wolf bitch which gave birth to three cretin litters while 
apparently well but mated to a goitrous male. These facts 
concerning the etiology are given merely to emphasize the 
high degree of probability that the distribution of the 
lesions of the thyroid gland among our specimens indi- 
cates the susceptibility of the various orders. This per- 
haps needs no emphasis for the carnivores, but it does for 
the marsupials. The literature contains many references 
to goitre in domesticated ungulates ; this would give the 
impression that they are common among them, and so 
they may be, but this is not the case for wild migulates. 
There being no doubt that the Carnivora have the highest 
incidence of thyroid enlargement, man being especially 
prone to it, and since goitre may be induced in fish by 
