SPOROZOA 791 



SUB-CLASS NEOSPORIDA 

 SARCOSPORIDIA 



These organisms belong to the sub-class Neosporidia of the Sporo- 

 zoa, because the spore formation commences before the completion 

 of growth. They have been known since 1843, when Miescher dis- 

 covered " tubes " in muscle fibers, visible to the naked eye as fine, 

 white, opaque filaments. They have been found in deer, cattle, sheep, 

 swine, rabbits and man, and occasionally in birds and reptiles. Al- 

 though long known, our knowledge of them is still defective. In sheep 

 they are the cause of severe epizootics, and in mice they are fatal: 

 otherwise they seem to be harmless parasites and in rare instances 

 have been accidentally found at autopsy in man. 



The method of transmission is not definitely known. Theobald 

 Smith was able to infect mice with Sarcocystis muris by feeding mus- 

 cles from infected mice, and Darling was able to infect guinea-pigs 

 in the same manner. In nature it is probable that infection occurs 

 through the intestinal tract. They are exceedingly common in some 

 localities and may be seen in most abattoirs ; they have been found in 

 ninety-eight per cent of swine, ninety-eight per cent of sheep, and 

 commonly in deer and mice. 



To the naked eye they appear as whitish, opaque, cylindrical bod- 

 ies in the muscles lying parallel to the fibres. In the sheep, Sarcocystis 

 tenella reaches a length of sixteen mm., and in the deer cysts of fifty 

 mm. are found. In structure the l ' tube ' ' is seen under the microscope 

 to be composed of many sickle-shaped spores, called Eainey's cap- 

 sules. The tube has not a single cavity but a honey-comb or alveolar 

 structure, and the spores are found in small aggregations in the cham- 

 bers, completely walled off from one another. The tube itself has a 

 heavy striated wall, either secreted by the organism or composed of 

 altered muscle fiber of the host. The spores are sickle or kidney- 

 shaped and vary both among themselves and with. the host. They 

 contain a nucleated trophozoit, and at one pole either a clear or an 

 obliquely striated body. 



Laveran and Mesnil (1899) obtained a toxin from Sarcocystis 

 tenella and named it sarcocystin. Darling, working in Panama, found 

 this organism in the biceps muscle of a negro from Barbados. 



