1919 ] Boeck: Studies on Giardia Microti- 89 



found that the cysts were never in sufficient numbers to make the use 

 of this instrument practicable. The number of cysts were then counted 

 in any twenty fields of the microscope, using a one-inch ocular and 

 four-millimeter objective. The following table (1) shows the occur- 

 rence of the cysts in the faeces and the count that was made. The 

 examinations commenced October 25, 1917, and were concluded Novem- 

 ber 21. 1917. 



This table is a record of the daily examination of the faeces of 

 the differenl rats, with the number of cysts counted in any twenty 

 fields of the microscope. A negative sign signified that no cysts were 

 found in the faeces for that day. 



Prom a study of table 1 it will be seen that rat number 7 was nega- 

 tive for all tin' examinations. It received five treatments of magnesium 

 sulphate in a. twenty-five per cent solution and no cysts or living 

 Giardia were seen in the semi-fluid stools. It was concluded that this 

 rat was not infected with Giardia. Cysts were found in the faeces of 

 rat 3 for three successive days, after which there was no recurrence. 

 In rat 15 cysts appeared November 8 and not again until November 

 20 and 21, when the examinations for all the rats were concluded. 



In the study of the rats in table 1, to determine whether or not there 

 was evidence for a cycle of encystment, the data for rats 3 and 15 were 

 not considered since neither showed two complete periods when cysts 

 were ejected and consequently no interval could be determined between 

 successive appearances of cysts. The data for rats 1, 2, 4, 5, 6, 8, 9, 10, 

 11, 12, 13, and 14 are the only data, then, that were used in this study 

 of periodicity in the appearance of the cysts. 



The length of the period during which the cysts were defaecated 

 with the faeces varied from one to fourteen days, and the interval 

 during which no cysts were found in the faeces varied from one to 

 eleven days. There is a common feature seen in the records of most 

 of the rats in that the ejection of cysts occurred at three or four 

 periods during the twenty-eight days of daily examinations. The 

 highest count of cysts was recorded on November 21 in the examina- 

 tion of the faeces of rat 14. There were eighteen cysts in twenty 

 fields of the high power objective. 



The data for each one of the rats was plotted so that each graph 

 resulting would represent more clearly the evidence for the presence 

 of a cycle of encystment in Giardia microti. The points on the ab- 

 scissa represent the days when the examinations were made, while the 

 points on the ordinate represent the number of cysts counted in twenty 



