280 BULLETIN OF THE BUREAU OF FISHERIES. 



cool weather. If the fish have not been greatly weakened by unfavorable conditions, 

 especially lack of oxygen, treatment with i to 1,000 copper sulphate just before they are 

 liberated in the river would doubtless cause a marked decrease in the loss from disease. 

 Some experiments were attempted along this line in September, 1919, but owing to an 

 accident the results were of no value. 



EXPLANATION OF FIGURES. 



All figures, with the exception of figure 249, are from photographs by the author. Abbreviations 

 used are as follows: bl, blood; cor, corium; ep, epidermis; and mus, muscles. 



Figs. 231 and 232. — Crappie, Pomoxis sparoides, with dorsal, caudal, and anal fins infected. Note 

 lesions just starting in three places on anal fin of fish in figure 232. 



Fig. 233. — Bluegill, Lepomis incisor, with dorsal, caudal, and anal fins infected. 



Figs. 234 and 235. — Fingerling buffalofish, Ictiobus bubalus, with caudal fins badly infected. 



Fig. 236. — Largemouth black bass, Micropterus salmoides, showing infection on dorsal, anal, and 

 caudal fins. 



Fig. 237. — White bass, Roccus chrysops, with infection developing on dorsal, anal, and caudal fins. 



Fig. 238. — Bullhead, Ameiurus melas, with a number of small lesions on dorsal surface of body. 



Figs. 239 and 241. — Bullheads, Ameiurus melas, in late stages of the disease. 



Fig. 240. — Bullhead, Ameiurus melas, with nearly entire side of body covered with lesions. 



Fig. 242. — Small bullhead, Ameiurus melas, with posterior end of the body infected and another 

 lesion just back of pectoral fin. 



Fig. 243. — Head of crappie. Pomoxis sparoides, with operculum removed to show small lesion on 

 gill. 



Fig. 244. — Head of buffalofish, Ictiobus bubalus, with operculum removed to show a somewhat larger 

 lesion on gill than in figure 243. 



Fig. 245. — Head of buffalofish, Ictiobus cyprinella, with operculum removed to show gills in late 

 stages of the disease. 



Figs. 246 and 247. — Bacillus columnaris. From a dried smear stained with carbolfuchsin. X Soo. 



Fig. 248. — Small portion of scale of bluegill to show formation of columns by bacteria along the 

 edge. Photomicrograph from preparation mounted in glycerin jelly and stained with eosin. Columns 

 are more slender and pointed than normal, due to shrinkage by the preserving fluid. 



Fig. 249. — Showing formation of columns by bacteria along edge of a bit of infected tissue after 

 being removed to slide. Somewhat diagrammatic. X340. 



Figs. 250 to 257 are from cross sections through' lesions in integument of bullhead, Ameiurus melas. 



Fig. 250. — Lesion just beginning to develop. X 7°. 



Fig. 251. — A little later stage in development of lesion. The epidermis is entirely destroyed at 

 one place to the right in the figure. X 70. 



Fig. 252. — A somewhat later stage than figure 251. The corium is beginning to disintegrate where 

 the overlying epidermis has been destroyed. X 70. 



Fig. 253. — Cross-section through lesion in late stage of disease. The corium is entirely destroyed 

 at center of lesion. Less highly magnified than preceding figures. 



Fig. 254. — Showing disintegration of epidermis in early stage of development of lesion. X 108. 



Figs. 255 to 257. — Sections through margin of well-developed lesions, the epidermis at the right 

 has been entirely destroyed. Note the blood corpuscles (bl) in the outer layer of the corium and between 

 the corium and the epidermis. In figure 255 the blood has broken through into the epidermis for a 

 short distance. X 108. 



Fig. 258. — Inclosure constructed of poultry netting in which fish were held in experiments 6, 7, 

 and 8. 



Fig. 259. — Small pond from which fish were taken in experiments 6 and 7. 



