118 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



Lieberkiihii^ believed that such amci-boid organisius attack tbeinselves 

 to the skin for the purpose of reproduction. Ludwig-' thinks that the 

 greater frequency of occurrence on the gills indicates a greater ease 

 of infection through this channel than via the alimentary canal. Also 

 he says: 



The lymph channels of the -conuective tissue appear to represent the principal 

 paths through which the parasite spreads itself further through the body. 



He, however, fails to give any actual evidence in favor of this view. 



Pfeifter ^ says : 



The common occurrence of the Myxosporldia iu all organs presupposes a distri- 

 bution via the circulatiou, a mode demonstrated by the infection of the red blood 

 corpuscles.'' 



Effects. — Upon this Balbiani^ has the following: 



Unlike the Gregarines and the Coccidia, the psorosperms spread themselves through 

 almost all the organs, the deep as well as the superficial, the skin, spleen, kidney, 

 air bladder, and even the heart and ovary. They are also found in the cells of the 

 urinary tubules, and in the young Graafian follicles, which they transform into a 

 pocket filled with psorosperms. As at the same time they increase with great rapid- 

 ity, it results that animals thus infested present grave diseases and may even die. 

 Certain morbid states of fish ought without doubt to be attributed to the Myxospo- 

 ridia. Such is the case of that Merluche' observed by J. Miiller and which was 

 remarkable for an extraordinary emaciation. I have myself often seen roach, tench, 

 and other fishes reduced by these parasites to a cachectic state characterized by a 

 decoloration of the tissues, destruction of the red blood globules, and augmentation 

 of the white globules; a veritable leucocythiemia. It is not, then, surprising that 

 this disease can cause great ravages among fishes, above all in the young, which are 

 most often affected. Nevertheless this cause is not usually noted as among those 

 which destroy fishes. This is easily explained; wlien the disease reigns attempts are 

 first made to explain it by macroscopic causes and ordinarily it is the worms which 

 are accused. This was the case iu the epidemic of the tench in the etangs of Dombes ; 

 it was the Ligules'which interfered with digestion and the fishes died of inanition. 

 Microscopic causes are not the ones most frequently suspected. I believe that more 

 frequent search would reveal microscopic lesions capable of explaining the mortali- 

 ties of young fish, particularly those living in marshes and in aquaria. 



Upon this point M. Thelohan ^ remarks that these parasites are gen- 

 erally well borne, but that sometimes the tumors may cause death by 

 pressure effects, e. g., he saw a cyst in Gasterosfeus aculeatus produce 

 fatal pressure upon the heart. 



The principal extensive epidemics have been those involving the 

 barbels and the crayfishes (see pp. 197, 231). 



1 Miiller's Archiv., 1854, p. 357 (see also p. 185). 



2 Jahresber. d. rhein. Fisch.-Vereins, 1888, pp. 33-4. 



^Die Protozoen als Krankheitserreger, 1890, 1 ed., p. 48. 

 ■• For the latter see p. 288. 



6 Journ. de Microgr., Paris, 1883, vii, pp. 280-281. 



6 1 have elsewhere noted this error (p. 172). The fish in question is Gadiis morrhiia 

 and not Merlvcius merlucius. 



^Aimal. de Microgr, 1890, li, p. 203. 



