endothelial and lymph cells. Both Delhi boil and kala-azar are 

 thought to be transmitted by insects. Infection of vertebrate 

 hosts by Herpetomonas and Crithidia yields pathogenic results for 

 mammals. The organisms assume both flagellated and non- 

 flagellated forms resembling Leishmania. 



Spirochaetes are slender wavy cells, with lateral non-undu- 

 lating membrane. The nucleus is represented by a series of 

 chromatin bodies, and there is a characteristic formation of internal 

 spores, indicating that the cells may be bacterial and not protozoan. 

 Several species have been studied in freshwater and marine molluscs 

 and in birds and mammals. Spirochaeta duttoni is the causative 

 agent of African tick fever, an important human disease distributed 

 through the Congo State and elsewhere in Africa. The organism 

 is found in the blood and is transmitted through the medium of a 

 tick, Ornithodorus moubata. In the body cells of the latter the 

 spirochaete breaks up, releasing a large number of minute "coc- 

 coid" bodies which pass out with the excretions of the tick and 

 appear to reach the human host in this way. These bodies are 

 also present in the eggs of the intermediate host. 



Recurrent or Relapsing fever of European countries is also a 

 spirochaete disease, the organism being 5. recurrentis . It is pre- 

 sumably transmitted from the bodies of lice which are crushed on 

 an excoriated surface rather than through the bites of the insects 

 themselves. 



Two forms of spirochaetes, S. buccalis and S. den Hum, are 

 known to occur in the human mouth, neither one being, however, 

 pathogenic. 



The treponemata are slender wavy or spiral threads without 

 membrane. The chief form is Treponema pallidum. It is the 

 causative agent of the loathsome but widespread disease of the 

 urinogenital organs, syphilis. T. pertenue is the agent in the human 

 disease of warm countries known as framboesia or yaws, charac- 

 terized by raspberry-like excrescences of the face and other parts 

 of the body. 



The parasitic Infusoria may for convenience be considered in 

 two divisions: (a) The natural group Tentaculifera, as distin- 

 guished from ordinary Infusoria or Ciliata, contains peculiarly 

 specialized tentacle-bearing forms {Acineta, etc.), the embryos of 

 which are ciliated and become parasites in the cells of other pro- 

 tozoa, (b) Ciliates parasitic in various higher animals, including 

 man. The chief human parasite is Balantidium coli. It is an oval 

 ciliated organism, with an oral depression at the anterior end of 

 the cell, meganucleus and micronucleus, and two contractile 

 vacuoles. It is the chief causative agent in ciliate (balantidian) 



