88 University of California Publications in Zoology [Vol.19 



ficance as a diagnostic factor in the detection of cysts. The amount 

 of stools defaeeated each day varied and on no day did the rats fail 

 to pass any stools. 



In the examination of the stools for the first four days a modifi- 

 cation (Boeck, 1917) of the method of faecal examination described 

 by Cropper and Kow (1917) was used. The method in its modified 

 form is as follows : To at least one gram of faeces add thirty cubic 

 centimeters of normal salt solution and stir with a Hamilton-Beach 

 "cyclone" mixer for ten minutes. Then add five cubic centimeters of 

 ether and stir for two minutes longer. The suspension is then placed 

 in a separatory funnel and allowed to stand for five to seven minutes, 

 during which time the two liquids will separate, the ether carrying 

 most of the debris to the top while the cysts remain in the normal 

 salt solution below. The normal salt solution is then drawn off into 

 a centrifuge tube of a capacity of fifteen cubic centimeters and centri- 

 fuged for three minutes. The cysts are concentrated at the bottom 

 of the tube and the supernatant fluid is drawn off with a pipette. 

 A drop of neutral red solution, one part to ten thousand parts of dis- 

 tilled water, is added to a drop of the residue from the bottom of the 

 tube and transferred to a slide for microscopic examination. The 

 cysts are readily detected with a one-inch eye-piece and a four milli- 

 meter objective. The cysts measure about fourteen microns in length 

 and six to seven microns in diameter. 



The other examinations were made by making a suspension of the 

 stools in distilled water, and stirring them until the mixture appeared 

 uniform in density. Again a drop of neutral red solution of the same 

 dilution as in the previous method, was added to a sample of the faecal 

 suspension, which was then examined under the microscope for cysts. 

 The neutral red is of great service in that it differentiates the cyst 

 from the yeasts and debris, which in most cases are partially or totally 

 stained while the cysts are very seldom affected by the stain and so 

 stand out in the preparation as clear, transparent, ovoid bodies. The 

 cysts also reveal in many instances their two or more nuclei, also the 

 remains of the axostyle, intracytoplasmic flagella, and the parabasal 

 bodies. 



There is no doubt that the concentration of the cysts by the ether- 

 centrifuge method is superior in accuracy to the simple microscopical 

 examination described in the preceding paragraph, but because of the 

 number of rats under observation this shorter method was used in this 

 work. A count of the cysts was also undertaken at the time examina- 

 tions were made. At first a haemocytometer was used, but it was 



