THE SPOROZOA 



301 



sarcoplasm, the latter having greatly increased in amount, its 

 nuclei multiplying by direct division (Laveran and Mesnil [119]). 

 The parasite then passes from the substance of the muscle into 

 the adjacent connective tissue, still surrounded, however, by a 

 secondary coat derived from the muscle-fibre, in which the nuclei 

 disappear. Thus the parasite is found under two phases, which 

 have been given distinctive names under the impression that they 

 represent distinct genera, the first lodged in the muscles (Miescheria), 

 the second in the connective tissue (Balbiania). 



In the second phase the parasite rounds itself off more, and 

 the tissues of the host form an adventitious cyst round it. The 

 cysts are conspicuous objects, often reaching a length of 16 mm. 

 in the sheep, while in the roebuck (Cervus capreolus) cysts of 

 50 mm. in length have been observed. Within the cyst are formed 

 vast numbers of minute germs (Fig. 120), either true spores or the 

 so-called " Rainey's corpuscles " (see below). The cysts are observed 

 to degenerate in some cases, their adventitious walls becoming 

 calcified, as the result of a defensive process on the part of the 

 host. Probably these are cysts containing spores, which can only 

 develop in another host. In other cases, the cysts burst and 

 spread their contents in the surrounding tissues, destroying the 

 muscles and producing tumours and abcesses within which the 

 parasite is found in the condition of "diffuse infiltration," like 

 many Myxosporidian parasites. It is in this stage that the con- 

 sequences may be dangerous or fatal to the host. The symptoms of 

 Sarcosporidiosis in the pig are " paralysis of the hinder extremities, 

 a skin-eruption, and general symptoms of sickness, such as thirst, 

 increased body -temperature, and dim, streaming eyes." 1 The 

 disease is sometimes the cause of fatal epidemics amongst domestic 

 animals, especially sheep. In the mouse also Sarcocystis muris is 

 a very deadly parasite. Mice attacked by it are distinguished 

 by their puffy, bloated appearance (Koch [118]), and are soon killed 

 by it. 



Many observations tend to show that the dangerous effects of 

 the Sarcosporidian parasites are not caused merely by the dis- 

 turbances which they set up ,in the tissues of the host, but are 

 due to an active poison secreted by the parasite itself. The 

 indefatigable French naturalists, Laveran and Mesnil [120], 

 have succeeded in isolating the toxin of the Sarcosporidian 

 parasite of the sheep, and have named it sarcocystin. This 

 substance is found to be extremely toxic to the experimental 

 rabbit, since a demimilligramme of the fresh extract, containing 

 y 1 ^ milligramme of solid matter, kills one kilogramme of rabbit, 



1 Quoted from Wasielewski [7], from whom many other facts stated here are 

 taken. The skin-eruption has an interesting parallel in the Myxosporidian disease 

 of the barbel (see p. 278). 



