HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



is due to a deficiency of protective bodies in the mucous 

 membrane of the young hosts and the development of 

 immunity in the older animals. 



Wagener (1924) secured evidence that the severity 

 of the infection depends on both the age of the host 

 and the amount of material injected. Thus young kittens 

 exhibited symptoms in from 2 to 5 days and frequently 

 died on the fourth day; whereas adult cats did not be- 

 come dysenteric for a week or more and lived for over 

 two weeks after definite symptoms developed. Two adult 

 cats remained alive and passed amoebae for six weeks 

 and a half -grown cat recovered and its stools became 

 amoeba-free. The infection in kittens although more se- 

 vere was limited to the rectum; in adult cats the entire 

 area from the ileo-cecal valve to the anus was eroded. 



It seems certain that resistance to infection and to the 

 pathological effects of tissue invasion is acquired as the 

 host grows older, but the nature of this resistance is 

 unknown. 



Does infection with amoehce of the same or a different 

 species add to tlie resistance of the host? Kessel (1923) 

 answers this in the affirmative. He found that young 

 rats that were infected with rat amoebae were more diffi- 

 cult to infect with human amoebae than those that were 

 amoeba-free, indicating that resistance to human amoebae 

 is built up by a foreign host that is infected with its 

 "normal" species. 



Climate. Climate (see p. 81) is often called upon to 

 explain host susceptibility to histolytica infection. The 

 fact to be explained is the greater number of clinical 

 cases of amoebiasis in the tropics than in temperate re- 



102 



