THE SARCOSPORIDIA 757 



by a thin membrane and the genus Sarcocystis the intra-muscular species which 

 had a thick capsule penetrated by fine canaliculi. The genus Balbiania comprised 

 the parasites found in the connective tissues and these had a thin cuticle. These 

 so-called genera are, however, merely stages in the life history of the same parasite 

 (Laveran and Mesnil). 



FIG. 359. Section through a muscle infected with Sarcocystis tendla. 



Sarcosporidia can be most conveniently studied in the muscles of sheep 

 and pigs in which they are sometimes found in enormous numbers chiefly 

 in the oesophagus, tongue, psoas and diaphragm. 



If a portion of an infected muscle be examined under the microscope the 

 parasite will appear as a whitish fusiform or spindle-shaped body measuring 

 1-5 mm. long lodged in the muscular fibre, its long axis running in the long 

 axis of the muscle. These elongated spindles represent Miescher's or Rainey's 

 tubes [so called after Miescher, who discovered sarcosporidia in the muscles 

 of mice and after Rainey, who found similar parasites some years later in 

 pigs' muscles]. The membrane enclosing these tubes is at first a fine, struc- 

 tureless cuticle but before long it thickens and becomes channelled by numerous 

 very fine canaliculi (arranged for the most part transversely to the long axis 

 of the parasite, but towards the extremities directed obliquely and at the tip 

 lying in the direction of the long axis). The extreme tenuity of the membrane 

 (ca. 1/x) can be demonstrated in sections of sarcosporidia (Laveran and Mesnil). 



As the parasite grows it gradually distends and destroys the muscular fibre 

 in which it is parasitic, until finally it is surrounded merely by the sarcolemma 

 and sarcoplasma and drops out in most cases into the connective tissue. 

 This then is the way in which the intra-muscular parasite (Sarcocystis) 

 becomes the connective tissue parasite (Balbiania). 



While the parasite is growing at the expense of the muscular fibre in which 

 it has taken up its abode the nucleus divides into a number of secondary 

 nuclei around which the protoplasm segregates, thus forming a number of 

 sporoblasts which in turn segment, giving origin to the so-called falciform 

 corpuscles or sporozoites. 



On leaving the muscle arid passing into the connective tissue the spindle- 

 shaped parasite is surrounded by a second capsule derived from the muscular 

 fibre (Laveran and Mesnil).' It now changes its shape, becomes rounded, 

 and at the same time increases in size (up to 1 cm.) by an increase in the 

 number of sporozoites, while its cuticle or membrane is so distended as to 



