1919] Boeck: Studies on Giardia Microti 131 



in both these rats at autopsy, showed them to be free from infection by 

 this flagellate. 



It would seem that these two rats, 8 and 10, were cured by the action 

 of the chemicals, but such a conclusion is not altogether warranted 

 when we consider that the other four rats remained infected. Another 

 interpretation of these two cases is justifiable, viz. : In the study of the 

 cycle of encystment in G. microti rat 3 showed only one period when 

 the cysts were found in the faeces. At autopsy this rat proved to be 

 free from an infection by Giardia and the conclusion reached was that 

 the rat had been capable of ridding itself of the infection, one way or 

 another. 



It will be noticed that in the cases of rats 8 and 10, w^hich appeared 

 cured by the chemicals, treatment with these salts of bismuth did not 

 take place until December 18. This date was twenty-six days, approxi- 

 mately four weeks, after the day when their period of infection of 

 twenty-eight days, November 21, had been concluded. There was an 

 interim, then, of nearly four weeks during which these two rats could 

 have thrown off the infection. 



If rats 8 and 10 threw off the infection previous to the treatment 

 with the salts of bismuth then all the days subsequent should have 

 showed no cysts in the faeces. This, however, was not the case for 

 rat 8 showed cysts in the faeces on two successive days, December 27 

 and 28, and rat 10 showed cysts in the faeces on December 22. A 

 possible explanation of the presence of these cysts may be that they 

 are perhaps the result of a short period of reinfection. 



Reinfection might have occurred by the transfer of pellets from 

 rat 9 into the cages of rats 8 and 10. Rat 9 escaped from its cage 

 one night and was found the next day running along the cages of 

 the other rats. If reinfection took place then, according to the data 

 both rats 8 and 10 must have thrown off the infection for the second 

 time for no cysts were in the faeces after the single period of infection 

 in either of the rats and they were not present at autopsy. 



Even though reinfection might have taken place it is altogether 

 probable that the salts of bismuth did cure these two rats; but the 

 persistence of the infection in the other four rats certainly militates 

 against the practicability of these chemicals as a specific cure for 

 giardiasis. 



Porter (1916) reports the cases of three men infected with G. intes- 

 tinalis and treated with bismuth salts in which an apparent cure was 

 affected. It is significant to note that daily faecal examinations of 



