78 American Fisheries Society. 



aeed two to three years, in waters more distantly removed 

 from hatchery discharges have been found to be "carriers" 

 of the orofanism, though, at the time of observation, apparently 

 quite unaffected by it. 



It is reasonable to suppose that immunity is relatively high 

 in wild waters compared with that under hatchery conditions, 

 where recurring waves of the disease have been observed after 

 the peak of the epidemic is passed, and where its reappearance 

 occurs among two-year-olds that have successfully passed 

 through the first attacks. But it is certain that before any 

 broad generalization can be made on the degree of resistance 

 that infected trout may acquire to Octomitus after planting in 

 wild waters more extensive study of the problem is necessary. 



In passing to the discussion of the third and last subject, 

 the life history of the organism, I shall make use of the ac- 

 companying charts (Figs. 1 and 2) , which illustrate in the one 

 case, the mechanism of the disease, and in the other, the more 

 formal representation of the life cycle so far as it is known. 



THE MECHANISM OF THE DISEASE. 



By reference to the chart (Fig. 1) it is seen that the seat 

 of infection where fatal lesions are produced lies in the fore- 

 intestine. Here the epithelial or lining cells of ceca and in- 

 testine (C, D and Di) are shown harboring the parasite in 

 various stages of development, from exceedingly minute 

 juveniles less than a micron in diameter to those of 9-12 mic- 

 rons in diameter, ready for emergence from the cells as typi- 

 cal fiaG:ellated adults. The time interval required to pass 

 through the intracellular stao-es is undoubtedly brief, for dur- 

 ing an epidemic the fatal lesions develop rapidly. From the 

 intracellular stage the parasites pass into the adult form 

 emerging into the lumen of the intestine on the dissolution or 

 disintegration of the parasitized cell. It can be imagined from 

 the diagram, which for purposes of clearness illustrates only 

 a mild infection, that the drain on the parasitized tissue must 

 be very great when the number of encysted organisms is ex- 

 cessively high. 



As indicated, the stomach, fore-intestine, ceca and blood 

 seem to be involved in the cj^cle of development. The occur- 

 rence of the organism in the blood indicates the possibility of 

 egg infection from brood fish that are "carriers." 



Juveniles (A) are presumably set free in the stomach on 

 ingestion and germination of a spore, the resistant structure 

 concerned in the transmission of the organism. The mode of 

 ■progress from this point to encystment in the epithelial cells 

 Of the fore-intestinal region is not yet clearly established 

 though the observation that the blood corpuscles seem to be 



