382 BULLETIN OF THE BUREAU OF FISHERIES. 



the tumor, deposition of pigment and final clearing up of these phenomena with total 

 disappearance of the tumor, leaving only a small residue of approximately normal 

 functionating thyroid alveoli, presents a picture which can be readily distinguished from 

 the characteristic appearance of colloid goiter, as found in the Scotch sea trout. From 

 the evidences obtained from the fish from the Algonquin National Park, we are of the 

 opinion that trout in the wild state may also suffer from simple hyperplasia of the thyroid, 

 which also, no doubt, would terminate by resolution in colloid goiter, although we have 

 not been fortunate enough to secure such specimens from the wild state. As the majority 

 of the Scotch sea trout under the conditions we have studied present both in the small 

 fish and in the adults a preponderance of strictly normal thyroids, it is obvious that this 

 condition is not the direct result of domestication, the existence of simple hyperplasia 

 in wild fish making this deduction obvious. 



Whether simple hyperplasia leading to colloid goiter in the Scotch sea trout is a 

 process with distinctive etiology, possibly the result of unusual physiological demand 

 upon the organ, or a greatly modified type of carcinoma of the thyroid occurring in 

 an immune species, can not at present be determined. The observation in one or two 

 of the older fish of red floors, and one or two reported tumors which we did not see, 

 may indicate that further material may be secured which will throw light upon this 

 question. For the present we would recognize a simple hyperplasia not associated etio- 

 logically with carcinoma of the thyroid. 



PATHOLOGIC ANATOMY. 



GROSS ANATOMY. 

 EARLIEST MACROSCOPIC EVIDENCE. 



The first evidence of thyroid proliferation visible to the unaided eye is the so-called 

 red floor (fig. 23 and 23a). It is a faint reddening or flushing of the median area of the 

 floor of the mouth usually opposite to or in the neighborhood of the second gill arches. 

 It is caused by the increasing blood supply of the main thyroid deposit and by hyper- 

 emia of adjacent tissues, which show through the epithelium. Its first appearance is 

 sometimes a mere streak, more often a circular or irregular diffuse reddening. It usually 

 soon spreads more widely, reaching a little out on the arches and tending to spread 

 forward toward the first pair of arches, and is, of course, variable. At the angles between 

 the arches the color is often heightened and very distinct. The color picture illustrating 

 the red floor shows a well developed process scarcely prior to visible swelling, and not 

 the very earliest flush of hyperplasia. The color changes rapidly under examination 

 on account of the excitement of the fish due to removal from water and the vigorous 

 handling necessary. The red flush pales rapidly under these conditions and often almost 

 disappears in less than a minute, due to the inhibition of the circulation from nervous 

 shock, the area taking on a dirty gray color. 



The red-floor stage is not sharply demarcated from the succeeding stages. It pro- 

 ceeds gradually and is succeeded by or merged with visible tumor formation, the color 

 persisting and spreading in various degrees over the subsequent swelling. 



