1128 REPORT OF COMMISSIONER OF FISH AND FISHERIJ-.S. [2] 



suffering from this so-called ''pox," I found that the hitter was a local 

 thickening of the epidermis, a condition of things to which Von Sie- 

 bold^ had first called attention. During the spawning season such 

 thickenings of the skin are frequently observed in male cypriuoids, par- 

 ticularly on the head, the cheeks, aud the gills, resembling whitish 

 wart-like ijrotuberances. This, of course, does not exclude the possi- 

 bility that such thickenings of the epidermis, under certain hitherto 

 unknown circumstances, may develoi) as actual pathological growths. 



On the other hand the " spot-disease," *. e., the appearance of white or 

 bright spots on the epidermis of fishes, is invariably caused by animal 

 parasites, in fact by iufusoria. This " si)ot-disease" will make its ap- 

 pearance not only among freshwater fishes, but also among those living 

 in salt water. When I examined a Mustelus vulgaris Milil. and Henle, ■ 

 and an Acanthias vulgaris Eisso, both afflicted with this disease, I 

 tbuud the cause ol" the spots to be infusoria which, living in the pulp- 

 cavity of numerous placoid scales, had absorbed their contents, pig- 

 ment cells, «&c., as nutriment, and had consequently produced colorless 

 patches on the skin. The rapid decay of the fish unfortunately pre- 

 vented me from making a more thorough examination of this species of 

 infusorians. 



Ililgendorf and Paulicki, of Hamburg, were the first to report the 

 existence of infusoria as parasites on the skin of freshwater fishes.'' In 

 the aquarium of the Hamburg Zoological Garden the "appearance of 

 slimy excrescences, finally assuming a fungus-like appearance, aud 

 (pausing the <leath of the fish," was observed in 1808 in many difl'erent 

 kinds of fishes in the freshwater tanks. The above-mentioned natur- 

 alists discovered in the epidermis, which had become thickened owing 

 to the fungus-like growth, small infusoria, measuring about 0.5 milli- 

 meter in diameter, which at first were only considered as occurring 

 casually, but which, on closer examination, were found to be the cause 

 of the disease. Hilgendorf and Paulicki could not discover in these 

 infusoria either a mouth or cilia of any (lonsiderable size, or any char- 

 acteristic sha|)e of the body. The cuticle was covered with very fine 

 evenly-developed cilia, arranged in long, gently-curved lines standing 

 close together. All that could be recognized in the body was a nucleus 

 (in large specimens having the shape of a horseshoe), the contractile 

 vesicle, vacuoles, and granules. According to Hilgendorf and Paulicki, 

 these infusoria appertain to a genus termed by Ehrenberg Fantotrichum. 

 In some of them, which had gathered at the bottom of a glass vessel, 

 the process of fission was observed. In my opinion Hilgendorf and 

 Paulicki very correctly consider the appearance of the infusoria as the 

 primary, and the development of fungus as the secondary, process. 



This entire process resembles very strongly another phenomenon ob- 



^ Von Siebold: "Die SUsswasserJische von Mittel-Europa." Leipsic, 1863, p. 89. 

 'Dr. F. Hilgendorf aud Dr. A. Paulicki: '^Infusionsihiere als HautparaHiten hei Siiss- 

 waaserjiiichen,*' in CentralhlaU fiir die Mtdicimschen Wisacnischafien, 1869, No. 3, p. 33 . 



