2o8 RESEARCH IN PROTOZOOLOGY 



Disturbances accompanied by marked evidence of reaction to in- 

 flammatory and toxic processes are of bacterial origin. 



Disturbances manifested by evidence of proteolytic destruction 

 of tissues, bemorrhage and mild simple inflammatory reaction of 

 a secondary nature, are caused primarily by animal organisms. 



Our unsolved problems, real and fancied, fall into a group of 

 disturbances that is not sharply marked off in this manner. They 

 have been stated by numerous v^^riters, sometimes fairly conserva- 

 tively, but often with gross extravagance. Out of a large number 

 of such papers that I have read in the past few years I have 

 selected two which illustrate what I mean. I refer to the papers 

 of Smithies (1926) and of Barrow (1924). 



Host-parasite relationships have been discussed in this volume 

 and elsewhere by Hegner, and I have touched on the matter of the 

 chemistry, evolution and general theory of these relations in other 

 publications (1914, 1918, 1920). Much of this matter is rather 

 speculative, but it will be well for the student to go over it in 

 formulating his problem. 



THE INTESTINAL FLAGELLATES AND THE QUESTION OF THEIR 

 PATHOGENICITY 



There is evidence that under certain conditions, so far not ascer- 

 tained, some trichomonads will wander from their natural habitat 

 in the intestine to other parts of the body of their host. This makes 

 the case of this flagellate the most interesting of our borderline 

 problems. Haughwout and de Leon ( 1919) have reported finding 

 TricJwmonas and spirochetes in the exudate aspirated from the 

 pleural cavity of a Chinese in Manila. However, careful study of 

 sections of the lung and pleura failed to disclose any in these 

 situations. The origin of the flagellates in this case is extremely 

 uncertain. The case reported by Kessel (1925) is more convincing. 

 He found Trichomonas in the exudate from the liver of a Korean 

 at operation for hepatic amoebiasis. It seems not unlikely that they 

 accompanied the amoebae from the intestine to the liver through 

 the portal circulation. Wenyon's discovery (1920) of Trichomonas 

 in the mucosa of the intestine at autopsy furnishes some evidence 

 that this flagellate is capable of invading the tissues of man. It 

 is singular, however, that other similar findings have not been 

 made. It already has been shown by Haughwout and de Leon 

 (1919), Kofoid and Swezy (1924), and others, that P entatrichom- 



