672 INTESTINAL PROTOZOA AND HOST-PARASITE RELATIONS 



pyorrhea alveolaris, but there is no evidence that this is actually the case, and at 

 present this species must be included with the other harmless commensals. 



HOST-PARASITE RELATIONS OF INTESTINAL FLAGELLATES 



There are seven well-authenticated species of so-called intestinal flagellates that 

 live in man. One species, Trichomonas vaginalis, occurs in the vagina of women and 

 the urinary tract of men, and another, Trichomonas huccalis, lives in the mouth. The 

 other five have been found only in the intestine. 



1. Trichomonas vaginalis. — Various investigators have reported from lo to 50 

 per cent of the women examined in various parts of the world to be infected with this 

 organism. Only a few cases have been reported of infections in men. The method of 

 transmission of this species is still in doubt. Both men and women may become in- 

 fected during coitus. If the intestinal trichomonad and the vaginal trichomonad are 

 one and the same species, a point that is not yet definitely established, the vagina 

 may become infected by contamination with organisms from the intestine. 



Very little is known regarding the pathogenicity of Trichomonas vaginalis. It has 

 been reported most frequently from women suffering from some abnormal condition, 

 especially when the reaction of the vaginal mucus is acid. Treatment with sodium 

 bicarbonate has been recommended by certain physicians who have reported favor- 

 able results. The only lower animal in which vaginal flagellates have been reported 

 appears to be the monkey, Macacus rhesus. 



2. Trichomonas huccalis. — The trichomonad that inhabits the mouths of about 

 one-third of the human population is considered by many protozoologists to be a 

 distinct species to which the name Trichomonas huccalis is given. Transmission no 

 doubt occurs during kissing. Recent studies by Hogue (1926) and Hinshaw (1926) 

 indicate that persons suffering from pyorrhea, acute gingivitis, or abscessed teeth 

 are more frequently infected than those whose mouths are in a normal condition. 

 There is no real evidence, however, that this flagellate is in any way responsible for 

 the pathological conditions with which it is associated. Trichomonads have recently 

 been reported from the mouths of dogs and cats (Hegner and Ratcliffe [1927a, 19276]) 

 but have not been recorded from any other lower animal. 



3. Trichomonas hominis. — The transmission of Trichomonas hominis is of peculiar 

 interest because there is no cyst stage in the life-cycle of this species, and hence new 

 infections must be due to the ingestion of food and drink contaminated with material 

 containing trophozoites. It has been suggested that Trichomonas huccalis that lives 

 in the mouth may be the same as the intestinal species and bring about infection in 

 the intestine when swallowed. This is not true, however, since individuals have been 

 noted who harbored the mouth species but were free from the intestinal form. Further- 

 more, there are certain morphological differences between these two types. Experi- 

 ments performed by the writer (Hegner [1924 and 1926]) prove that several species 

 of trichomonads are capable of passing through the stomach and small intestine of 

 rats and guinea pigs without apparently affecting their viability, and no doubt T. 

 hominis can pass through the stomach and small intestine of man without injury. 



The incidence of infection with T. hominis in the general population, as reported 

 in the literature, is much lower than actually exists. This is due to the fact that much 



