HOST-PARASITE RELATIONS! INTESTINAL PROTOZOA 



almost complete reversal from acidophilus to putrefac- 

 tive bacteria within the intestine due to the carnivorous 

 diet effected changes in the contents unfavorable for the 

 flagellates. Tsuchiya (1925), however, has found large 

 numbers of trichomonads in certain human cases irre- 

 spective of whether the food was largely of a carbohy- 

 drate or protein nature and his conclusion is that "The 

 type of intestinal flora does not alter the number of 

 flagellates." Herbivorous and omnivorous animals no 

 doubt more frequently ingest food contaminated by the 

 feces of others of their kind than do carnivorous species ; 

 but the latter would probably become infected if flagel- 

 lates were capable of living in their intestines. Conditions 

 within the large intestine of carnivores must be par- 

 ticularly unfavorable to bring about a resistance so ex- 

 treme as to prevent flagellates from obtaining a foot 

 hold in this habitat during the course of evolution. 



(3) Pathogenicity. Many protozoologists believe 

 that trichomonads are merely commensals or "food rob- 

 bers" that have found the large intestine of man a 

 favorable place in which to live. In this habitat they feed 

 on food particles taken in by the host, or on bacteria, 

 and absorb the products of digestion through their body 

 wall. Growth and reproduction occur until enormous 

 numbers of organisms are present, some of which are 

 carried out of the body in the feces and keep the race 

 from dying out by infecting new hosts. On the other 

 hand, a considerable body of evidence has been accumu- 

 lated, principally by physicians, that these flagellates 

 actually attack the host and bring about what is known 

 as trichomoniasis or flagellate diarrhea. Many cases of 



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