1919 1 Boeck: Studies on Giardia Microti 87 



of each flagellate, then cysts should be present in every one of the 

 hosts in which the examination of the large intestine had been made. 

 (The large intestine is the region of the digestive tract in which cysts 

 occur in greatest numbers.) Again, if encystment occurs at all times 

 then cysts should always be found in faeces of rats infected with 

 Giardia, and the number of cysts in the faecal sample of a rat should 

 be approximately the same for each day. The process of encystment 

 would then be an even, regular process from day to day and would 

 not show evidence of a sudden rise and fall in the number of cysts 

 found in the faeces. 



The enumerations of the cysts of G. intestinalis in human dysen- 

 teric faeces made by Porter (1916) gave for the first time critical evi- 

 dence of a cycle of encystment in this flagellate, which is a species allied 

 to G. microti. 



The importance of knowing whether or not there is a cycle of 

 encystment in these flagellates cannot be overestimated. It would be 

 of great significance in the therapy of dysentery caused by these 

 organisms as well as a considerable factor to reckon with in the 

 diagnosis of dysenteric patients by the daily examination of their 

 stools, if a more or less regular cycle should be found to occur. It 

 would be necessary to make a longer series of examinations in order to 

 determine whether or not a patient were infected if a cycle of encyst- 

 ment is present in the life history of the flagellates causing the dysen- 

 tery than it would if no such cycle were present. Accordingly daily 

 examinations of the faeces of fifteen rats were begun and carried on 

 throughout a period of twenty-eight days for the purpose of securing 

 if possible sufficient additional evidence to definitely determine the 

 facts. 



Materials and Methods 



The faecal pellets of the rats vary in size from the average, about 

 twelve millimeters in length and six millimeters in diameter, to about 

 four millimeters in length and two millimeters in diameter. Constipa- 

 tion was present when the pellets of the smallest size were defaecated. 

 The small size of the pellets could not be correlated with the absence 

 or presence of cysts within them. At no time were the faeces liquid 

 in consistency. There is no evidence of diarrhoea in the rats infected 

 with Giardia like that caused by G. intestinalis in man and mice. The 

 color of the faeces was usually a dark brown. Variations in the color 

 from darker shades of brown to very light yellow were of no signi- 



