Figure 10: — Photomicrograph of l"^os oina 

 cerebralis in cartilage at U months 

 post-infection. Note that two spores 

 develop in each pansporoblast. Stained 

 with Giemsa's to show spores (x U30). 







# 



^ 



n 



4i( 



Figure 11: — Photomicrograph of Myxosoma 

 cerebralis in cartilage at U months 

 post-infection. Stained with Giemsa's 

 to show spores (x 970). 



Figure 12: — Free-hand drawing of t^osoma 

 cerebralis pansporoblasts containing 

 two spores each. Four months post- 

 infection. 



Eight months and older (figs. 13 and 14) 



At this time all of the pansporoblasts have 

 produced their spores, and these can be seen in 

 the "lesion". Apparently the rest of the para- 

 site disintegrates. The spores appear to re- 

 main in the lesion site permanently- -Uspenskaya 

 (1957) found them in 3-year-old fish. We have 

 found many spores in 2 -year -old fish and pre- 

 sume that they may remain much longer. It has 

 been assumed that the spores remain in the site 

 of the lesion, but she cites evidence that some of 

 them are transported, presumably by blood, to 

 other organs including the liver and lumen of the 

 intestine. We believe that this is not the usual 

 means of spore dissemination. 



HISTOPATHOLOGY 



There is no evidence of histopathology 

 during the incubation period of 40 to 60 days . 

 However, after this, as the trophozoite grows, 

 cartilage is eroded, skeletal support is weaKen- 

 ed, and simultaneously there is a proliferation 

 of epithelioid-type granuloma about the parasite 

 and its spores. 



10 



