HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



(1915b) states that some specimens of human tricho- 

 monads become spherical and motionless when removed 

 from the body and in this condition "will withstand the 

 action of gastric juice for a considerable time," and ex- 

 presses the opinion "that it appears probable that it is 

 such contracted spherical forms which are responsible 

 for the spread of the infection," but apparently did not 

 carry out any infection experiments. Woodcock (1917) 

 also suggested that "infection with trichomonas can take 

 place by means of the active, unencysted forms." Ex- 

 perimental evidence that trophozoites of trichomonads 

 are capable of passing unharmed through the stomach 

 and small intestine and of setting up an infection in the 

 large intestine of a mammalian host is now available. 

 Experiments with rats, guinea-pigs and cats. Infec- 

 tion experiments carried out by Hegner (1924a) with 

 Trichomonas miiris of the rat prove that trophozoites 

 of this species are capable of remaining actively motile 

 for at least one hour after being injected into the 

 stomach of the rat ; that they may pass from the stomach 

 into the duodenum apparently unharmed within half an 

 hour ; that they may reach the cecum through the stomach 

 and 780 mm. of small intestine within half an hour and 

 still be actively motile; and that a rat free from tricho- 

 monads may acquire a cecal infection within four days 

 after trophozoites are injected into the stomach. Later 

 experiments (Hegner, 1926c) prove that the tropho- 

 zoites of Trichomonas cavice and T. flagelliphora of the 

 guinea-pig are able to pass through the stomach and small 

 intestine of a guinea-pig and reach the cecum apparently 



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