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. Peipus and Ladoga. 
Heciting causes —This may be safely assumed to be the presence and 
development 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 fish vitality that the 
reactive encapsuling of the parasite is no longer possible. The latter 
then obtains the supremacy, and through the accompanying bacteria 
rapid death of the fish may result. 
Mégnin’s opinion is as follows: 
Mode of infection.—One now understands how the fish become infected; the psoro- 
sperms which escape from the ulcers are ingested with the water during deglutition 
or respiration; under the form of an amcboid they enter the circulatory current, 
then arrive in the subcutaneous cellular tissue, which is their seat of election, where 
they undergo their last transformations. 
Upon this subject Ludwig remarks that— 
The greater frequency of occurrence upon the branchiw 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 epidemic? It is diffi- 
cult. Isee no other method than to collect all the dead or sick fishes 
and destroy them by fire” (Mégnin). 
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 prophylactic 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 Myzosporidia 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 reéntry 
of the germs into the water. 
1 Die Protozoen als Krankheitserreger, 1890, 1 ed., p. 67; 2 ed., 1891, p. 110. 
2No actual observations are cited in support of this lymph-path theory. 
3 Pfeiffer (loc. cit., 1 ed., 1890, p.37) quotes Ludwig as recommending that they be 
buried. 
