314 University of California Publications in Zoology [Vol. 20 



Another difficiiltj' is correlated with the change in habitat of the 

 cysts of these organisms on discharge in the stool. If the seat of 

 infection is the ujDper part of the colon where the conditions differ 

 somewhat from those prevailing in the rectiim and stool, such differ- 

 ences undoubtedlj' react on these delicate organisms so that only those 

 protected by a fully developed cyst may pass out of the body without 

 showing some of the deleterious effects of this great environmental 

 change. Such changes as those incident to passing from the region 

 of the mucosa to the lumen and thence downward in the stool appear 

 to be associated with the process of encystment. It is also possible 

 that changes in the temperature of the environment or in available 

 oxygen may temporarily' suspend or accelerate developmental changes 

 within the organism, such as mitosis, until a more favorable location 

 is reached, when normal development may again proceed. 



It is evident to anj' one who works over amoebic cysts that a vary- 

 ing number of the cysts ordinarily met with in stool examinations 

 sliow the results of degenerative changes, particularly if the specimen 

 has remained in the laboratory some time before examination. In 

 any consideration of the various stages of the life history, these forms 

 must be eliminated or the results will be disastrous from a cytologieal 

 standpoint. It is also doubtful how much value can be placed on the 

 cytologieal study of the amoebae which have been inoculated into 

 kittens, since an alien host may tend to produce some morphological 

 changes. 



Endamocha coli is a common infection of man but is rarely present 

 in great numbers in human stools. The different stages of mitosis are 

 seen only occasionally and are rare in the cysts in most stools. It is 

 therefore difficult to make a sufficient number of observations of 

 mitosis in the cysts of this human intestinal amoeba to use as a basis 

 for the investigation of this process. 



The material on which this studj^ was made, and from which the 

 figures illustrating it were mainly drawn, was found in a single stool 

 from an overseas ex-soldier in the University Infirmary. It occurred 

 among more than one thousand stools containing infections of E. coli 

 which were examined among more than six thousand routine examina- 

 tions with a total of four thousand two hiuidred persons. A fresh 

 stool was available and many of the cysts were found with mitosis 

 in progress. An attempt was made to secure further development 

 by keeping the stool in a warm oven and making slides at intervals 

 of a few hours. In the first set made, the slides showed two and four 



