322 RESEARCH IN PROTOZOOLOGY 



gills by Myxoholns or Henneguya apparently disturbs the respira- 

 tory function of this organ in such a way that the host fish suc- 

 cumbs to the infection. The muscles are the seat of infection of 

 several species of myxosporidia. Perhaps the most thoroughly 

 studied form is Myxoholus pfeifferi which attacks the muscles and 

 connective tissue of various organs of the barbel and other fresh- 

 water fishes in European waters. Conspicuous boils appear in 

 heavily infected fish, hence this myxosporidiosis is known as "boil 

 disease" (Pfeiffer, Thelohan, Keysselitz, etc.). The boils are 

 principally located in the body muscle which condition hinders the 

 movement of the infected fish. When the boils become large, the 

 color and luster of the body surface are lost, the scales fall ofif, 

 and the host finally dies. At the beginning of the infection, the 

 muscles appear yellowish in color and are soft and gelatinous. Such 

 a fish has a bitter'taste when cooked, and hence has no commercial 

 value. According to Thelohan and Keysselitz, the direct change 

 which the infected muscle fiber manifests, is a hyaline degeneration 

 of the fibrils. Davis (1924) recently finds that the so-called 

 "wormy" halibut along the Pacific coast of North America is due 

 to an infection of the muscle fibers by an intracellular myxospor- 

 idian, Unicapsula muscularis. Elongated vegetative forms of this 

 myxosporidian are found to be present in a single row within the 

 entire length of the fiber. They, however, do not extend to the 

 sarcolemma, "there being always a thin layer of sarcoplasm and 

 muscle fibrils between the two." Davis found that the muscle fibers 

 showed little sign of injury in spite of the abundance of the 

 parasites. But the infected fibrils become swollen and undergo a 

 hyaline degeneration ; no fibers have, however, been observed in 

 which fibrils were entirely destroyed. 



The circular muscle fibers of the small intestine of a black 

 crappie which were in direct contact with the cysts of Myxoholus 

 intestinalis were seen by the writer (Kudo, 1929) to become sepa- 

 rated from one another and to turn about ninety degrees from their 

 original axial direction. These fibers become undulating fibrillar 

 structures which later degenerate completely. 



Lentospora ccrcbralis is now generally recognized as the 

 causative organism of "Drehkrankheit" of salmonid^ and 

 GADiD^ through the studies of Hofer and Plehn (1904, 1924). 

 According to Plehn, young fish are particularly susceptible to 

 infection. The posterior region of an infected fish loses its normal 



