[Light and electron microscope studies on cysts of Sarcocystis fusiformis in the muscles of calves infected experimentally with oocysts and sporocysts of the large form of Isospora bigemina from cats (author's transl)].

In several experiments young calves were infected with oocyss and sporocysts of the large form of isospora bigemina from cats, which has been fed by raw beef containing Sarcocystis fusiformis cysts. On he 98th and 160th day p.i. the calves were killed and the development of S. fusiformis cysts in muscle cells was sutided by lign and electron microscopy. The cyst was always situated within a muscle fiber which was never surrounded by fibrillar layers of host origin (= no secondary cyst wall). The cyst was limited by a singel unit membrane, which was thickened at numerous places of the interior by osmiophilic material. This complex is called primary wall (Primärhülle), reaching a thickness of up to 250 A. This primary wall was regulary folded, forming palisade-like protrusions...