Boech: Studies on Giardia Microti 



101 



examinations comprising less than one-half the total number of exam- 

 inations. The graphs of figures 3, 4, 6, 12, and 14 fall into this class. 

 In the second group may be placed all the other groups ; in these more 

 than one-half the total number of examinations were positive. 



What caused this great difference in the degree of the infection 

 in the rats is not known at the present time for there is no evidence 

 at hand with which to attack this problem ; but it is very significant 

 that, even when the positive examinations comprised less than half 

 the number of all the examinations which were made, there are still 

 distinct periods into which the positive examinations fall. 



3 4 5 6 7 



10 11 12 13 14 15 



Fig. 15 



Frequency curve of modal intervals. 



Curve (solid) plotted by single-day units (on abscissa) of the day intervals 

 between the modes of all the figures 1, 2, 4, etc. 



Curve (broken) plotted by two-day units, of the day intervals between modes 

 of all the curves. It is a more typical frequency curve. 



The interval (average) between modes is shown to be seven days. Seven 

 days is the interval then, between the maxima number of cysts in the faeces. 



This graph represents the combined plot of the intervals between 

 the modes of all the curves described in the preceding pages. The 

 units on the abscissa stand for the length, in days, of each interval; 

 the units on the ordinate stand for the frequency with which any 

 given interval occurred. 



The solid line is a frequency curve whose descent is characteris- 

 tically lytic in nature ; the latter feature is eradicated if only the out- 

 side points are represented in the curve. The broken line curve was 

 made from the same data as the solid line curve except that the units 

 on the abscissa are two days in length instead of a single day. This 



