OF THE ALIMENTARY TRACT 17 



portant factor in determining the growth of such 

 parasites after their introduction. 



In this connection an observation of the writer in 

 the production of experimental intestinal amoebia- 

 sis in the rat is, perhaps, worthy of note. Rats fed 

 on stale w^hite baker's bread exclusively w^ere more 

 readily infected than those on a more varied diet and 

 the colitis found was more extensive and active. 



The relation of the diet to the development of para- 

 sitism of these organisms and, further, to the effects 

 produced upon the host by the parasite is a promis- 

 ing problem for investigation. 



ENCYSTMENT 



Most of the protozoa of the alimentary tract, as 

 is the case in general with protozoa, are able to form 

 about their bodies a resistant capsule, when condi- 

 tions are not favorable for continued vegetative 

 existence in their environment. In some this en- 

 cystment is consonant with preparation for multipli- 

 cation, so that w^hen again ready for activity the 

 animal emerges from the cyst in the form of its 

 offspring. 



Immediately prior to encystment there is a slowing 

 up of the movement of the body and usually con- 

 traction to smaller size, extrusion of food materials 

 from the body, and, in some, a slow revolvement of 

 the body while the cyst is forming. This contracted 

 stage is the ''precystic" form. 



