300 



THE SPOROZOA 



individuals, however, only naked gymnospores appear to be 

 produced, probably serving for multiplication of the parasite 

 within the host. 



(a) Occurrence, Habitat, etc. The Sarcosporidia have so far been 

 found, with few exceptions, 1 only in warm-blooded vertebrates. 

 In mammals they occur very frequently in domestic animals, and 

 are nearly always to be found in the pig and the sheep. They 

 also occur commonly in the horse and ox, and have been found in 

 a number of other mammals, including the human species. 2 In 

 birds they have been found in domesticated species, such as the 

 common fowl and duck, and in wild birds, as, for example, the 

 blackbird. 



The earliest stage of the parasite which has been observed is 

 lodged within the substance of a muscle-fibre in the form of an 

 elongated body known as a "Miescher's Tube" (Fig. 117). The 

 muscles affected are more especially those of the trunk in the 

 vicinity of the stomach ; the muscles of the oesophagus are the 

 chief seat of the parasite (Fig. 116), 

 then those of the larynx, the body- 

 wall, and the diaphragm, and the 

 psoas muscles. In acute cases all the 

 skeletal muscles may be infected, 

 even those of the head. Sometimes 

 the parasites are found in the eye- 

 muscles. Within the muscle - fibre 



FIG. 116. 



Sarcosporidia in the ox ; a transverse 

 section of the oesophagus, natural size, 

 showing the parasites in the outer (a, 6, 

 c, d, e)and inner (/, g, /i)muscular coats. 

 (From Wasielewski, after Van Becke.) 



FIG. 117. 



Longitudinal section of a 

 muscle-fibre containing a Sarco- 

 sporidian parasite, X60. (From 

 Wasielewski, after Van Eecke.) 



the parasite grows until it distends the fibre to five or even ten 

 times its normal breadth, absorbing the contractile substance as it 

 does so. Finally, it is surrounded only by the sarcolemma and 



1 The exceptions are Sarcocystis platydactyli, described by Bertram from the 

 muscles of the gecko, Platydactylus mauritanicus, and a species observed by Liihe in 

 the lizard Lacerta muralis. 



2 For the recorded cases of Sarcosporidiosis in man, see Smith [121], p. 1, and 

 Vuillemin [122], p. 1152. 



