OBSCURE PARASITES 195 



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, Chlamj^dozoa. 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 

 above, are caused by protozoan parasites is very doubtful, and 

 only further investigation can determine the true status of their 

 causative microorganisms. The fact that typhus fever and 

 infantile paralysis were until very recently looked upon as quite 

 as probably caused by protozoan organisms as some of the diseases 

 named above, and that this opinion has been reversed as the result 

 of work done in the last two or three years (1914-1917), would 

 make it not at all surprising if more of the obscure or invisible 

 parasites of these diseases should be shown to be bacterial in 

 nature, rather than protozoan. 



