1919] 



Boeck: Studies on Giardia Microti 



95 



10 



were not cleaned of their faeces each day after the last faecal exam- 

 ination had been made. The cysts which might have caused this 

 reinfection may have entered the cage by dropping through the wire 

 netting with faecal pellets. On two instances an infected rat became 

 free from its cage and ran over tops of the others and it is very likely 

 that a few of its pellets could have dropped into the cages of the 

 other rats. 



Rat 8. There are three periods and an incomplete fourth when 

 the cysts were found in the faeces. The mode of the first period occur- 

 red on October 27. The period of depression between this mode and 

 the mode of the next period when cysts were in the faeces is very 

 w^ell defined in that the curve decreases abruptly from mode one until 



i 



i 



i 



u 



25 25 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 



Eat 8 

 Fig. 7 



on October 31 no cysts were found in the faeces, then the curve rises 

 again until the second mode is reached on November 3. The period 

 of depression between the second and third mode is defined by four 

 negative examinations. The third period of cysts in the faeces com- 

 mences on November 4 and continues until November 16. Two maxima 

 appear in the portion of the graph, and both of them have been termed 

 modes since there is a distinct period of depression on November 12, 

 but it is possible that we have in reality a single mode in this period. 

 The next period starts on November 18 and was continuing when the 

 last examination was made ; but because of this last mode five may not 

 be the true mode of this period ; instead the last one may be only a 

 stepping-stone to another mode which would have been reached if the 

 examinations had continued a greater length of time. The intervals 

 between the modes are 7i/2, 5%, 5, and 4 days, respectively. 



