1919] 



Boeck: Studies on Giardia Microti 



105 



been possible to continue the examinations by means of the ether- 

 concentration method, adopted Inter, then three ordinary examinations 

 would not have been necessary, one examination by this method would 

 have sufficed. 



Again, in all the studies of this nature the more cases one works 

 with the safer are his conclusions ; therefore, if a greater number of 

 rats could have been handled the conclusions would have a greater 

 degree of certainty. But even with this relatively small number of 

 cases, when the results are to a great extent uniform, the conclusions 

 are at least highly significant and to a considerable degree may 

 be relied on as presenting the truth of the situation. The data from 



8 9 10 11 12 13 14 

 Fig. 18 



16 17 18 19 20 21 22 23 24 25 26 



Frequency curve of mode intervals; data taken from charts submitted by 

 Porter (1916). 



Solid line, interval plotted by single-day units, modes at 8, 15, 24. 



Broken line, interval plotted by two-day units, modes at 6, 9, 14. 



The broken line curve, a typical bi modal polygon. 



The interval between the maximal number of cysts is about 7-8 days. Four- 

 teen days represents two intervals, and the small mode at 24 represents three 

 intervals. 



These results from studies of seven cases of Giardia intcsiinalis are very 

 similar to those given by me for G. microti. 



the fourteen rats presented by several methods yield in every ease the 

 same fairly uniform and equivalent cycle of encystment. 



Another source of evidence is available for comparison to demon- 

 strate the value of these results in this small number of cases. In 

 determining the cycle of encystment for Giardia intestinalis from 

 man and mice Porter (1916) noticed that there was a period of about 

 a fortnight between the maximum number of cysts recurring in the 

 faeces. She did not, however, call attention to the fact that there 

 was also a period of about seven- or eight days when another maximum 

 number of cysts was to be found in the faeces. This she would have 

 found apparently if the day-interval between the modes in all her 

 figures had been plotted. 



