CHLAMYDOZOA 2O/ 



The pustules are most common on the head and fins, but occur also on the eyes and 

 gills of the host. The young parasite, which is one of many formed in a cyst, is very 

 small. At first it is free swimming, but soon attaches itself to the skin of a fish. It 

 bores inwards and becomes surrounded by the irritated skin. There it attains a 

 relatively large size, being 500^10 750/4 and occasionally more in diameter. The 

 body has a rounded terminal mouth, short cytopharynx and a number of minute 

 contractile vacuoles. The macronucleus is large and horseshoe-shaped ; the small 

 micronucleus is only seen in the very young animal. When full grown, the organism 

 encysts and forces its way to the surface and bursts through, leaving a small, gaping 

 wound behind. The cyst sinks to the bottom of the water, nuclear multiplication 

 occurs and a number of young parasites are produced, which leave the cyst and 

 either attack new hosts or else perish. 



Opalina ranarum, parasitic in the rectum and urinary bladder of frogs and toads, 

 shows great degradation and simplification due to parasitism, possessing no separate 

 micronuclei, no cytostome, cytopharynx or cytopyge. It has many macronuclei, and 

 is a large parasite. During summer and autumn nuclear multiplication followed by 

 division of the body occurs, the process being repeated after the daughter forms 

 have grown to the size of their parent. In spring, the Opalina divide rapidly, but 

 do not grow much before dividing again. Finally, tiny forms, containing three to 

 six nuclei, encyst and pass from the host with the faeces. As these latter are greedily 

 devoured by tadpoles, the Opalina gain new hosts in which they develop. 



THE CHLAMYDOZOA. 



The name Chlamydozoa was proposed by Prowazek in 1907 for a 

 number of minute, problematic organisms (fig. 119) believed to be 

 the causal agents of certain diseases in man and animals, such as 

 vaccinia and variola, trachoma, inclusion blenorrhcea in infants, 

 molluscum contagiosum, and bird epithelioma contagiosum. Other 

 diseases possibly due to Chlamydozoa * are hydrophobia, measles, 

 scarlet fever, foot-and-mouth disease, the " Gelbsucht" disease of silk- 

 worms, and perhaps even typhus (Prowazek, 1913). The subject is 

 difficult and controversial and can only be briefly discussed here. 

 It is known that the viruses in all these diseases can pass through 

 ordinary bacterial filters, that is, they belong to the group of " filterable 

 viruses." At such periods the organisms are extracellular or free. It 

 is also known that in many of these cases the virus produces definite 

 and characteristic reaction-products or cell-inclusions in the infected 

 cells, during the intracellular phase of the life-history of the organism. 

 As the organisms to be considered are problematic, it will be con- 

 venient to summarize their history : 



(i) Cell-inclusions, usually named after their discoverers, have 

 been found in certain diseases, thus : In vaccinia Guarnieri's bodies, 



1 For a detailed account of the Chlamydozoa see Prowazek's Handbuch der Pathogenen 

 Frotozoen, Bd. i (1911-12). Leipzig, J. A. Earth. 



