508 



PROTOZOOLOGY 



may vary in size from microscopic to as large as 5 centimeters. They 

 are cylindrical with more or less pointed extremities and with a some- 

 what lobulated surface, and appear opaque whitish. They were for- 

 merly called Miescher's tubes (Fig. 238). The envelope around the 

 parasitic mass appears to rupture sooner or later and the spores are 

 set free in the blood stream and into the alimentary canal. The spores 

 find finally their way out of the host intestine and become the source 

 of infection (Scott). 





Muscle layer 



■^ Connective tissue layer 





Fibrous zone 



Externals 



Median / Cyst membrane 



Internal ) 



Sporoblasts 



Spores 



Fig. 239. Portion of a cyst of Sarcocystis tenella in sheep, X about 

 'lOOO (Alexeieff). 



As to the pathogenic effect of the parasites upon the host animal, 

 fatal cases are not uncommon. In heavily infected animals extensive 

 muscular degeneration appears and the hosts die from the infection. 

 One peculiarity of the Sarcosporidia is that these organisms contain 

 certain toxin, sarcocystine which when injected is highly toxic to 

 other animals (p. 28). 



Genus Sarcocystis Lankester. In muscles of vertebrates; numer- 

 ous species have been described from various animals en the basis 

 of difference in host species and slight difference in dimensions of 

 spores. 



