CONTENTS. 

 j* 



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 junction 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 411 



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 hatchery, 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 



365 



