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University of California Publications in Zoology [Vol.19 



in the number of cysts then took place, but the cysts were not absent 

 from the stools until November 12. Two cysts were found on the fol- 

 lowing day, but none occurred on November 14. The third period of 

 cysts in the faeces began November 15, and although there was a 

 decrease in the number of cysts on November 18, to rise again on the 

 following day, this period may best be regarded as continuing from 



m 



tszt 



/ 



25 20 27 28 29 30 31 1 2 3 4 



6 7 8 9 10 11 12 13 14 15 16 17 IS 19 20 21 

 Rat 2 

 Fig. 2 " 



ffl 



/ 



\ 



25 26 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 3 

 Fig. 3 



November 15 to 21, when no cysts were found in the last faecal exam- 

 ination. The intervals between modes one and two, two and three, 

 are five and eleven days, respectively. 



Rat 3. There was only one period when cysts were ejected, Novem- 

 ber 5 to 7, and because they never recurred again the data from this 

 rat could not be used to contribute any evidence on our problem. 

 The rat was found free from infection at autopsy on January 9, 1918; 

 the organs were normal, and none of the lesions of the intestine were 

 present which characterize an infection by Giardia. The fact that 



