CHLAMYDOZOA 193 



hydrophobia (Fig. 59D). At first thought to be simple parasites, 

 these bodies are now generally regarded, as are other Chlamydozoa, 

 as reaction products of the host cell surrounding one or many mi- 

 nute granules which are the true parasites. The minute size of 

 the granules and the difficulty of identifying them when they are 

 separated from their " mantles " probably accounts for the 

 negative findings in infective parts of the nervous system in 

 which Negri bodies are not found, and also in the saliva, which is 

 highly infective. The weight of evidence seems to favor the 

 protozoan affinities of the microorganism of hydrophobia, but 

 the nature of the parasite is still shrouded in uncertainty. 



Trachoma. The belief in the protozoan nature of the parasite 

 of trachoma, a disease of the eyes causing inflammation of the con- 

 junctiva, rests on similar ground. In the affected portions of the 

 eye are found numerous tiny granules known as " Prowazek's 

 bodies " (Fig. 59C), sometimes within the cells and even within the 

 nuclei and < at other times free in the serum, which have been 

 thought to be the cause of the disease. The fact that these bodies 

 are sometimes found in other affections has thrown some doubt 

 on their relation to trachoma. Recent investigations by Anna 

 Williams of 4000 school children in New York with eye infec- 

 tions or inflammations, none of which were typical cases of " tra- 

 choma," showed " trachoma inclusions " to be common, and gave 

 evidence that these inclusions were in reality " nests " of growing 

 bacteria, of various kinds, in the epithelial cells of the conjunc- 

 tiva. Miss Williams' investigations throw doubt on the existence 

 of a specific disease to which the name trachoma can be applied. 



Other Diseases Caused by Obscure Parasites 



The diseases mentioned above are those which are most com- 

 monly thought .to be caused by organisms of this problematic 

 group, Chlamydozoa. There are a number of others, however, 

 which may belong here, but on which much further investigation 

 is necessary. Among. these are foot-and-mouth disease, in which 

 Stauffacher has recently found an organism, Aphthomonas infes- 

 tans, which, however, is probably more closely related to Leish- 

 mania (see p. 76) ; verruga peruviana, which in some respects 

 resembles smallpox; the ubiquitous measles; and a number of 

 diseases which are of rare or of more or less limited distribution. 

 That all of these diseases, or even all of those separately discussed 



