SMALLPOX, SYPHILIS, CANCER, ETC. 171 



of sporozoa is very great. Pfeiifer was the first to point 

 this out, and in 1887 he named the parasite, " Monocystis 

 epithelialis," after the gregarines of the earthworm. 



FIG. 48. ELEMENTS FROM VACCINATED CORNEAS, 1 (from Path. Soc. 

 Trans. 1895), guinea-pig's cornea 3rd day ; a, two epithelial cells, 

 one containing a parasite, and three free parasites ; b, Cytoryctes with 

 central clearing containing chroma tin ; c, ibid, with three mitoses ; 

 d, ibid, with chromatin in nuclear form ; e, parasite with scattered 

 chromatin granules and a separated segment ; /, ibid, subdivided 

 into nucleated segments. 2 (after A. Borrel, 1903), rabbit's cornea 

 8th day ; all the epithelial cells contain Borrel's " pseudoparasites," 

 really Cytoryctes passing from pycno- to chasmatoplasson state with 

 the appearance of small nuclei ; a leucocyte at a. 



