Scott. — On Cancer in Fish. 201 



Art. XII. — Note on tlic Occurrence of Cancer in FisJt. 



By Professor Scott. 



[Read before the Otago Institute, 9tli June, 1891.] 



Plate XVIII. 



The fish afflicted with this disease were all sj)ecimens of the 

 American brook-trout (Salmo fontinalifi) kept in confinement 

 in one of the ponds at Opoho belonging to the Dunedin 

 Acclimatisation Society. Males and females were alike 

 affected, and the diseased fish never recovered. Through the 

 kindness of Mr. Deans, the manager, I was able to examine 

 several specimens showing the disease in various stages of 

 advancement, and the following is a short account of the naked- 

 eye and microscopic appearances of the growth. 



In the earliest stages the ventral wall of the pharynx in 

 the middle line, a short distance behind the tongue, is seen to 

 be somewhat roughened, and raised in low irregular swelhngs. 

 At this stage notliiug is to be seen unless the mouth is opened 

 widely. As the tumour grows, however, not only does it 

 involve more and more of the pharyngeal floor, spreading also 

 to a slight extent laterally, and involving the ventral ends of 

 the gill-arches, but it ultimately shows itself externally as a 

 rounded pink lump on the isthmus in the angle between the 

 diverging branchiostegal rays. 



A microscopic section of the tumour shows all the stages 

 in the development of a carcinomatous growth. In parts a 

 purely glandular structure is seen — the glands apparently of 

 the acino-tubular type. Elsewhere, owing to proliferation of 

 the cells, the gland acini have become distended and irregular 

 in form (adenoma stage), while in large areas these over- 

 distended acini have, as it were, burst, and the liberated cells, 

 making their way into the stroma, infiltrate it, and all gland- 

 structure is lost (carcinoma stage). 



Of the two figures which accompany this note, the first 

 (PI. XVIII. , fig. 1) shows the floor of the mouth and pharynx, 

 as seen from above, of a fish sufi^ering from the disease. The 

 nodular character of the tumour is clearly seen. The second 

 shows a small portion of a section as seen under the inicro- 

 scope. A distended acinus is seen liberating a stream of cells 

 into the gland stroma (fig. 2). 



The occurrence of cancer in the lower animals has been 

 frequently noted of late years, and it is by no means so rare 

 among them as it was at one time thought to be. I have, 

 however, been unable to find any mention of its having been 

 noted in fish. 



