128 University of California Publications in Zoology [Vol. 19 



The treatments began on December 18, 1917, and continued for 

 three weeks, until January 8, 1918. The dose for man was a tea- 

 spoonful of either of the bismuth salts three times a day, and usually 

 after five to ten days of treatments the infection appeared to be cured 

 (Porter, 1916). This dose for man amounted to about 3.6 to 4 grams 

 of the chemicals each day. 



To arrive at dosage for the rats a dose was proportioned accord- 

 ing to the ratio of the body weight of man (about 146 pounds) and 

 the average weight of the rats (about 300 grams). This dose was 

 found to be about 20 milligrams each day. This was the first dose tried 

 with the rats, but was considerably increased as the treatments pro- 

 gressed (table 5). 



In making the daily faecal examinations of these six rats faecal 

 emulsions of the stools were prepared in distilled water each day 

 during the course of treatment. A drop of this emulsion was trans- 



N 

 ferred to a slide, adding to it a dr-op of neutral red solution _ 



(Boeck, 1917), and then the preparation was examined for the cysts 

 of Giardia. 



When the cysts were found their number was counted in any 

 twenty fields of the microscope, using a one-inch ocular and a four- 

 millimeter objective. A plus sign was placed in the square of the 

 table (table 5) for that day and the number of cysts counted was 

 placed above the sign. If no cysts were detected in the first cover- 

 slip preparation from the emulsion, after stirring the emulsion a 

 second preparation was made and by the same procedure a third 

 preparation if the second one turned out to be negative. At the end 

 of three preparations no cysts were detected, then the stools were 

 designated negative for that day, and a minus sign was written in 

 the square of the table for that day. If, however, cysts were found 

 in either the second or third preparation their number was counted 

 and a plus sign written in the square for that day, placing the number 

 of cysts counted above the sign and the number of the preparation 

 below the sign. It took three negative examinations to make a rat 

 negative for that day on which the stools were collected. 



The dose of twenty milligrams was first administered to the rats. 

 The dose was the same for the bismuth subnitrate and bismuth sali- 

 cylate. After seven treatments with a dose of twenty milligrams the 

 daily examinations still showed rats 1, 4, 9, and 12 to be infected, but 

 rats 8 and 10 showed no evidence of infection, there being no cysts in 



