130 University of California Publications in Zoology [Vol. 19 



the faeces. On December 25 the dose was increased to thirty milli- 

 grams for two days and then to fifty milligrams for three days, for 

 the fact that four rats remained infected led one to believe that the 

 dose previously used in the treatments was insufficient to effect a cure. 



After increasing the dose to fifty milligrams the crystals of the 

 bismuth subnitrate were seen in the faeces of rats 4, 9, and 10. The 

 dose certainly must have been adequate since the faeces contained a 

 great amount of the crystals, and the chemicals must have come in 

 contact with the flagellates. 



The rats appeared quite ill as a result of the large dose and the 

 treatment was dispensed with for two days. On January 1 a dose of 

 thirty milligrams was again administered and this dose was increased 

 to sixty milligrams on the following day. A dose of thirty milligrams 

 followed by fifty milligrams was given the rats on the next two suc- 

 cessive days. Treatment was suspended on January 5 and 6, and 

 sixty milligrams were given on the last day. 



At the end of this treatment with these two bismuth salts rats 

 1, 4, 9, and 12 were still infected. Cysts were found in the faeces of 

 all these rats, except rat 4 on the last day. But rat 4 showed cysts 

 in the faeces two days before the treatments were concluded. Only 

 rat 8, treated with bismuth salicylate, and rat 10, treated with bismuth 

 subnitrate, appeared to be cured. 



Discussion 



From table 4 we see that these two rats, 8 and 10, were heavily 

 infected during the twenty-eight days that their faeces were examined. 

 But during the treatment cysts were found in the faeces of rat 8 

 on only two different and successive days, while cysts were found in 

 the faeces of rat 10 only on one day. Apparently the drug had cured 

 these rats. 



The rats were then posted and at autopsy no sign of pathological 

 disturbance of the organs was seen. The jejunum, the seat of infec- 

 tion by Giardia in rats, was not discolored nor did it contain any gas. 

 In cases of infection the jejunum is usually orange colored and con- 

 tains gas. The upper and lower duodenum, jejunum, and ileum were 

 examined for free forms and cysts of Giardia and none were found, nor 

 were there any cysts in the colon or rectum. Oct omit us muris was 

 very abundant in the jejunum and ileum. The absence of Giardia 



