HOST-PARASITE RELATIONS I INTESTINAL PROTOZOA 



for a study of their viability. The eosin test has been 

 used for this purpose more than any other. Kuenen and 

 Swellengrebel (1913) were the first to use this method 

 to determine whether cysts are aHve or dead. Eosin in a 

 concentration of i :iooo appeared to penetrate and stain 

 dead cysts but not those that were alive. Later work by 

 Wenyon and O'Connor (1917), Cutler (1920), Yoshida 

 (1920), Root (1921), Boeck (1921a, 1921b), Bercovitz 

 (1924), Kessel (1925b) and others indicates that this 

 test is not infallible; dead cysts are usually stained but 

 some of them are not. Bercovitz (1924), for example, 

 found that cysts of Endamoeha coll that were killed by 

 chemicals did not, as a rule, take the eosin stain, and on 

 this account, employs hsematoxylin as a stain and cyto- 

 logical changes as a criterion of death. Boeck (1921) and 

 Kessel (1925b) showed that cysts that have undergone 

 plasmolysis do not become stained and Kessel was able 

 to prove that neither stained cysts nor the plasmolyzed 

 cysts of Hartmannella hyalina excyst in culture medium, 

 whereas most of the "green" (viable) cysts do. Root 

 (1921) found neutral red more satisfactory than eosin 

 since it stained a larger proportion of the cysts. Congo 

 red has also been experimented with by Bercovitz ( 1924). 

 The best method of determining whether cysts are alive 

 or dead is to test them in susceptible animals or in arti- 

 ficial culture. Now that culture methods have been per- 

 fected by Boeck and Drbohlav (1925a, 1925b) and 

 others, and excystation may be brought about in the test 

 tube, it will be possible to obtain more definite results than 

 heretofore regarding the longevity of cysts outside of 



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