94 



University of California Puhlications in Zoology ["^ol. 19 



remainder, for after this period there follows an interval of depression 

 when eight negative examinations occurred. The next period of cysts 

 in the faeces came on November 5, when the number of cysts increased 

 very suddenly to six, then fell to one on the next day, and remained 

 at two or one for the five following days. The mode of this period 

 came on the first day, when six cysts in twenty fields were counted. 

 No cysts were counted on November 15, but on the next day the num- 

 ber of cysts in the faeces began steadily to increase until the mode of 

 this period was reached on November 20, when ten cysts were counted. 

 The number began to decrease when the last examination was made. 

 The intervals between modes one and two, two and three, are eight and 

 twelve days, respectively. 



25 26 27 28 29 30 31 1 2 3 4 5 



10 11 12 13 14 15 16 17 18 19 20 21 



7 5 



Eat 6 

 Fig. 6 



Rat 6. This graph shows that two periods of cysts in the faeces 

 occurred. These two periods were recorded in the first eleven exam- 

 inations; the remaining examinations did not reveal any cysts. The 

 first period lasted only one day, while the second period lasted four 

 days. The interval between the modes of these two periods was six 

 days. 



This rat at autopsy on January 9 was still infected, even though 

 it had eighteen consecutive negative examinations. The organs were 

 normal except that there was a small amount of gas in the jejunum. 

 In other respects this autopsy was identical with that of rat 3. The 

 fact that this rat was still infected after having had eighteen consecu- 

 tive negative examinations showed that reinfection may have taken 

 place between the day when the last examination was made and the 

 day the autopsy was made. Reinfection was possible for the cages 



