32 PROTOZOAN PARASITISM 



e.g. in kissing, or through the intermediation of the 

 common use by mouth of the same materials, such as 

 in drinking, etc. On the other hand the amoebae 

 which inhabit the intestine must live through the 

 vicissitudes of passing out of the host, of external ex- 

 posure for varying periods of time and in contact 

 with various substances, and then through the di- 

 gestive juices of the upper alimentary tract, par- 

 ticularly the stomach, before reaching their natural 

 habitat again. Consequently encystment has been 

 necessary for their survival. In the important ones, 

 if not all of these amoebae, there is multiplication of 

 nuclei to a definite number during encystment, pre- 

 paratory to the liberation of its offspring. 



Reproduction in the vegetative phase is by binary 

 fission, with the production ordinarily of two indi- 

 viduals, this being the method of multiplication dur- 

 ing their natural life in the intestine. It is doubted 

 that the cysts hatch naturally until a new host is 

 invaded since the cysts are formed as the organisms 

 pass down the lower intestine to be excreted. 



METHODS OF EXAMINATION FOR AMOEBAE 



For study of the fresh active forms a portion of 

 the fluid content of the natural habitat of the organ- 

 isms is necessary. Depending on the consistency of 

 this medium it may be necessary to mix it with physi- 

 ological saline solution. The material should be 

 placed on a microscopic slide in thin enough state to 



