736 PATHOGENIC PROTOZOA 



elusions and becomes clear, transparent, and assumes a spherical form, 

 and secretes a cyst wall. The nucleus divides first into two, then four, 

 and finally eight daughter nuclei; there is usually a large vacuole 

 found in the cyst during this division, but its function is uncertain. 

 Schaudinn described a complicated autogamy in the cyst, yet later 

 researches by Hartmann and Whitmore show nothing more than re- 

 peated binary division of the nucleus. The normal number of nuclei 

 in a coli cyst is eight, yet occasionally cysts are seen in which division 

 has gone on until there are as many as sixteen. 



Cats or human beings may be parasitized by feeding material con- 

 taining coli cysts, and in nature, as the cysts are the resistant forms of 

 the parasite, the infection is probably transmitted from one host to 

 ^^^^^ another by means of them. No disease, 



however, results, though the amebae con- 

 / tinue to be present in the stools for years. 



It is possible that fertilization-takes place 

 &\ between the young ameba3 (gametes?), 

 which are liberated when the cyst dissolves 



. 



wi in a new host, as is the case with Enda- 

 meba blattas. 



ENDAMEBA GINGIVALIS 



FIG. 165.-ENDAMEBA COLI. < Gros 1849 > emcild - von ^owazek 1904) 

 Cyst showing eight nu- 

 clei. (Arch, fur Protisten- rhis ameba is found in the human 

 kunde, 1912, xxiv.) mouth both in health and disease. It has 

 been described at different times under 



various names (buccalis, dentalis) by Gros, Steinberg, von Prowazek, 

 Lewald, Smith and Barrett, Chiavaro and Craig, and quite recently 

 has been suggested as the cause of pyorrhea alveolaris by Smith and 

 Barrett and Bass and Johns. It is widely distributed, and has been 

 reported from all quarters of the world. 



The organism is easily found in the tartar at the base of the teeth, 

 in cavities in the teeth, and even at the gum margin in healthy mouths. 

 It varies in size from seven to thirty-five microns, averaging between 

 twelve and twenty (Craig). Motility is well marked, though it is not 

 so active an organism as histolytica, the pseudopods, mostly short and 

 blunt, being formed of the clear, slightly refractile ectoplasm. The 

 endoplasm is granular, contains the nucleus and many food vacuoles 

 containing nuclei of leucocytes and granular matter, and rarely a few 



