HOST-PARASITE RELATIONS! INTESTINAL PROTOZOA 



(1926) cases stool examinations by both smear and 

 culture methods proved negative. 



Infection and resistance. Transfer from one host to 

 another is no doubt the result of kissing and the flagel- 

 lates at some time probably reach the oral cavity of prac- 

 tically everyone. Failure to infect is due to the resistance 

 of the host, in other words, to the unfavorable condi- 

 tions that exist in certain individuals, or to non-aggres- 

 sive strains of parasites. That strains differ with respect 

 to their ability to withstand various conditions is in- 

 dicated by the work of Hogue (1926). Material was 

 subjected to heat for a certain period and then inocu- 

 lated into culture tubes. Two strains withstood a temper- 

 ature of 40° C. for 5 minutes, 2 strains 40° C. for 10 

 minutes, and 2 strains 45° C. for 5 minutes. Further- 

 more, certain strains lived for over 7 months whereas 

 others died out in 3 months in the same medium; some 

 persisted for 96 hours in a medium of pH 7.2-7.8 but 

 others were killed; and one strain was able to live in 

 normal saline solution to which horse serum was added. 



Host-parasite relations. Recent investigations indicate 

 a definite relation between the presence of T. buccalis 

 and a diseased condition of the oral region. Thus Hogue 

 ( 1926) found that all of her positive cases gave a history 

 of pyorrhea, acute gingivitis or abscessed teeth, and 

 Hinshaw (1926a) found no specimens in normal mouths 

 but records 37 positives from 49 patients with advanced 

 pyorrhea and no positives from 71 persons with normal 

 mouths or incipient pyorrhea. This flagellate, therefore, 

 seems to be associated with pathological conditions but it 

 is yet to be convicted of being responsible for pyorrhea. 



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