REPORT OF COMMISSIONER OF FISH AND FISHERIES. P25 
discovered protozoan parasite (Lymphosporidium trutte) to whieh the 
disease at the Commission stations bears a close resemblance in many 
respects. It was therefore thought that an examination of the patho- 
logical material from Northville and Manchester would probably 
reveal the same parasite. A careful search, however, failed to dis- 
close it, and the evidence pointed to the original diagnosis of bacterial 
infection, which was confirmed in the summer of 1901. It thus 
appears that the brook trout is subject to both bacterial and pro- 
tozoan infection, the two very similar in their external lesions. 
Studies were made of various minor cases of apparent parasitism 
or malformation in trout and of the blisters or air blebs of the mucous 
membrane of trout afflicted with pop-eye. Microscopic sections of the 
latter showed merely the method in which the superficial layer of 
epithelium had been uplifted by a gas pressure beneath it, and gave 
evidence of no more antecedent cause. As in the case of pop-eye 
among fishes in the Woods Hole aquarium, no parasite appeared in 
the immediate neighborhood of the gas accumulation, although this 
does not exclude, of course, bacteria difficult of demonstration or not 
demonstrable by ordinary methods. 
Of the other cases the most interesting was one of scarcely elevated 
black areas upon the skin of a brook trout, these having every appear- 
ance of parasitic cysts. On section, the black color appeared to bean 
increase in the normal pigment of the skin, while the elevation con- 
tained no parasites, many cocci-like bodies proving to be merely 
pigment granules. The slight elevation seemed to be caused by a new 
growth of normal tissue, and the most likely explanation is that the 
black spots are small neoplasms of uncertain classification. The 
same trout had asmall polyp or projection from the skin of the belly, 
which upon section appeared also to partake of the nature of a tumor. 
Pigment was absent from it, but is also absent from that portion of 
the belly. There is a possible relation between this process and the 
black cyst-like bodies upon the sides and back of the trout. 
Studies were made of the brain of salmon fry from the Pacific coast, 
which had died as so-called ‘‘crazy” fry, there being no external 
lesions or any circumstance whatever to account for the mortality. 
As brain pathology is of especial difficulty, and as but little is known 
of the microscopic features of the normal fish brain, not much was 
expected from this examination; but there was some evidence of 
brain lesions to account for the peculiar death of fry. These were 
not degenerations, but lack of complete development of important 
portions. If cases of this sort continue to arise, an important field is 
opened for study. 
An annoying fungus attack in the Commission aquarium at the 
Pan-American Exposition received some attention in June. The lake 
water was found to be charged with fungus spores, and the quantity 
used was too large to admit of a filtration that would remove these 
spores. It was concluded that the fungus could be kept in check 
