7GG SARCOSPORIDIA 



minute objects in their wanderings, and at the same time to exclude every 

 possibility of confusing them with portions of cell nuclei or other small 

 bodies in the tissues. 



Very little is known about the development of Sarcosporidia in other 

 animals. Bertram (1892) described young stages of the S. tenella of sheep. 

 The smallest forms consisted of elongate cytoplasmic bodies 4 to 5 microns 

 in length with a single nucleus. Older forms possessed a definite mem- 

 brane, and consisted of round or oval cells lying in spaces in a matrix. By 

 multiplication of thecells the spaces are enlarged and the matrix between 

 the spaces becomes the walls or septa of the chambers. When multiplica- 

 tion has produced the requisite number of cells in a chamber, they become 

 transferred into typical spores. 



Pathogenicity. — In the majority of cases, even when fairly heavy 

 infections exist, there is little evidence that the host is adversely affected. 

 Sheep have sometimes died with very heavy infections, and death has been 

 attributed to the Sarcosporidia. Creech (1922) has described extensive 

 muscular degeneration in pigs caused by these parasites. In experi- 

 mental mice the animals sometimes die, apparently as a result of intense 

 infection. A curious feature of the Sarcosporidia is that they appear to 

 contain a substance which is highly toxic to animals. Pfeiffer (1890) 

 showed that the parasites of sheep were highly toxic if injected into mice, 

 rabbits, and even sheep. Kasparek (1895) also showed that subcutaneous 

 injection of the sheep parasite killed mice and guinea-pigs. Laveran and 

 Mesnil (1899) made aqueous or glycerine extracts, and found that the 

 extract of 0-001 gram of fresh parasite when injected subcutaneously 

 killed rabbits in five to ten hours. Rats, mice, sheep, and frogs were not 

 affected. They named the toxin " sarcocystin." Similar experiments 

 were conducted by Rievel and Behrens (1904) with the Sarcosporidia 

 obtained from llamas. Teichmann (1910) used a dried extract of the 

 sheep parasite, which killed rabbits when injected intravenously in a dose 

 of 0-0002 gram dissolved in saline solution. Rats and guinea-pigs were 

 refractory. It was shown by Teichmann and Braun (1911) that rabbits 

 could be immunized against the toxin, and that the serum contained 

 antibodies which could produce passive immunity in other animals. 



Method of Infection.^ — Though it is easy to understand how infection 

 will spread amongst animals, such as rats and mice, which eat flesh, it is 

 difficult to see how this happens in the case of cattle and sheep, which are 

 nearly always infected and are purely herbivorous in diet. It occasionally 

 happens that in cattle the Sarcosporidia infect the skin, and recently 

 Sergent, Ed. (1921), has had the experience of finding the spores in blood- 

 films made from these animals after pricking the skin. He has raised the 



