Boeck: Studies on Giardia Microti 



91 



fields of the high power objective. Each one of these graphs will now 

 be discussed. 



Rat 1. This graph is plotted from the data of rat 1. Its modes are 

 very sharply defined since the periods of depression are characterized 

 by an absence of cysts. The first period when cysts were found in the 

 faeces lasted from October 29 to November 1. The mode of this part 

 of the curve was reached on October 30. A depression period of two 

 days when no cysts were found in the faeces ensued. This period 

 endured for three days. The mode recording the maximal number of 

 cysts occurred on November 5. A period when no cysts were found 



A 



i 



X 



z 



\ 



6 7 8 9 10 11 12 13 14 15 16 17 IS 19 20 21 22 23 24 25 20 27 2S 



Rat 1 



Fisr. 1 



in the faeces followed for four days, then there were two days when 

 one cyst was detected, followed again by an examination iu which no 

 cysts were detected. Another period of cysts in the faeces took place 

 from November 12 up to November 21, when the last examination was 

 made. The mode of this period came on November 15, while another 

 mode was in the process of formation because the number of cysts 

 was increasing when the last examination was made. The interval 

 between mode one and two is six days, and the second and third 

 modes are separated by an interval of ten days. 



Rat 2. This graph, made from the data of rat 2, is very similar 

 to the graph in figure 1, there being three modes in the curve. The 

 first mode occurred on October 31 when four cysts were counted in 

 twenty fields and the period of depression followed, during which the 

 number of cysts decreased to two on November 2. The cysts still 

 continued to be found in the faeces and their number began to increase 

 until another mode was reached on November 5. A sharp falling off 



