CONTENTS. 
Pa?a 
Introduction 367 
History of the present investigation 367 
History of the disease 369 
Normal thyroid in salmonoids 373 
Embryology 374 
Gross anatomy and distribution in the adult brook trout 376 
Anomalous deposits of thyroid 377 
Histology 378 
Simple hyperplasia and colloid goiter in wild and domesticated fish 379 
Pathologic anatomy 382 
Gross anatomy 382 
Earliest macroscopic evidence 382 
Visible tumors 383 
Branchial jimction 383 
Floor of mouth 384 
Pit tumors 384 
Histology 397 
Early stage 397 
Red-floor stage 398 
Visible-tumor stage — Structural types 399 
Infiltration 400 
Bone and cartilage ; vessel wall; muscle; skin 401-402 
Other observations 402 
Implantations and metastases 404 
Comparative pathology 407 
Occurrence of the disease under wild conditions 41 1 
Occurrence and course of the disease under domestication 413 
Distribution of the disease in United States hatcheries 413 
Names of species and hybrids 414 
Geological formation at fish hatcheries 415 
Chemistry of the water supplies 419 
Dissolved oxygen 420 
Endemic occurrence 424 
Caledonia hatcherj', New York 424 
Craig Brook station : Conditions at the beginning of the investigation 425 
Craig Brook station: Conditions during three years 428 
Lake Auburn hatchery, Maine 435 
Private hatchery in the State of Washington 436 
Epidemic occurrence 436 
60289° — Bull. 32 — 14 24 
365 
