132 University of California Publications in Zoology [Vol. 19 



these men were not made after the time the cysts disappeared from 

 the stools, following treatment with the chemicals. These men were 

 then discharged from the hospital as cured from giardiasis. Porter 

 recognized the presence of a cycle of encystmtent in G. intestinalis, but 

 this factor was not taken into account when the men were determined 

 free from infection. It is very probable if these men who appeared 

 cured could have been watched for several days longer and their 

 stools examined daily, that the cysts might have recurred. The fact 

 that the cysts were absent from the stools after several treatments 

 with the salts of bismuth was not conclusive proof that the men were 

 free from the infection of Giardia; this could only have been ascer- 

 tained by a series of daily examinations for the purpose of determining 

 whether or not the cysts recurred in the faeces at the proper time 

 in the cycle. 



Summary 



From the experimental work conducted with the salts of bismuth 

 on rats infected with Giardia and the results obtained with the 

 treatment of giardiasis in man with the same chemicals it is certain 

 that the therapeutic value of bismuth subnitrate and bismuth salicylate 

 is negative in the treatment of giardiasis. The conclusion is supported 

 by W. L. Yakimoff, W. J. Wassilevski, and N. A. Zwietkoff (1918), 

 who state the inefficacy of these chemicals in the chemotherapy of this 

 disease. 



