THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 233 



healthy whitefish sickened from introduction into water in which a 

 whitefish affected with myxosporidiosis had died, and as the same dis- 

 ease is not rare upon Coregonus from Lakes Peij)us and Ladoga. 



Exciting causes. — This may be safely assumed to be the presence and 

 dev^elopinent of the myxosporidia. Pfeiffer/ from numerous exami- 

 nations, states that these latter are always present in barbels from the 

 Rhine, Mosel, and Saar, becoming pathogenic only at irregular inter- 

 vals, probably when other causes so diminish lish vitality that the 

 reactive encapsuling of the parasite is no longer j)0ssible. The latter 

 then obtains the supremacy, and through the accompanying bacteria 

 rapid death of the fish may result. 



Megniu's opinion is as follows: 



Mode of infection. — One now understands how tho fish become infected; the paoro- 

 spernis which escape from the ulcers are ingested witli the water during deglutition 

 or respiration ; under the form of an amoeboid they enter the circulatory current, 

 then arrive in the subcutaneous cellular tissue, which is th«ir seat of election, where 

 they undergo their last transformations. 



Upon this subject Ludwig remarks that — 



The greater frequency of occurrence upon the branchiiB suggests that infection 

 occurs less through the alimentary canal than through the respiratory tract. The 

 lymph paths of the connective tissue appear to represent the principal channels by 

 which the parasite spreads through the body, but nothing certain is known. - 



The infection of previously healthy fishes is brought about, Pfeiffer 

 remarks, through the extensive fouling of the water by the numerous 

 fish corpses, and the durable construction of the spores. Infection may 

 then take place via the stomach, gills, or wounds. The last are of fre- 

 quent occurrence in the spring at the time of breaking up of the ice. 



Remedies proposed. — "How, now, to arrest the eindemic? It is diifi- 

 cult. I see no other method than to collect all the dead or sick fishes 

 and destroy them by fire" (Megnin). 



Ludwig thinks that our ignorance of the complete life-history of the 

 parasite, and especially of the way in which it secures a lodgment in 

 the fish, precludes rational radical measures and permits us only to 

 adopt certain proi^hylactic makeshifts. With reference to myxospo- 

 ridiosis, as also for a number of other reasons, the waters, especially the 

 Saar and Mosel, should be maintained in the highest state of purity, 

 and to that end all pollution of the rivers mentioned, by communities 

 or industrial establishments, should be interdicted. That most dan- 

 gerous contamination of the water, by the Myxosporidia from the ulcers, 

 cannot, of course, be stopped entirely, but it is evident that it will be 

 less if all fishermen are impressed with the importance of destroying^ 

 all diseased and dead fish, instead of throwing them back into the 

 water. Such destruction must be so effected as to prevent the reentry 

 of the germs into the water. 



'Die Protozoen als Krankheitserreger, 1890, 1 ed., p. 67; 2 ed., 1891, p. 110. 

 '^No actual observations are cited in support of this lymph-path theory. 

 =* Pfeiffer (loc.cit.,\. ed., 1890, p. 37) quotes Ludwig as recommending that they be 

 buried. 



