290 RESEARCH IN PROTOZOOLOGY 



This manipulation sends all of the oocysts to the bottom of the 

 tube. The supernatant fluid is carefully decanted, all of the sedi- 

 ment being retained. A boiled saturated solution of sodium chloride 

 is then added in small amounts, while the tube is gently shaken so 

 that the sediment is loosened and mixed with the saline. About 

 forty-five cubic centimeters of the solution are added in all. The 

 tubes are balanced by the addition of the saturated saline and are 

 centrifuged, at the same rate of speed as before, for not longer 

 than a minute. A portion of the upper layer of the mixture is 

 lifted ofif, by suspension across the mouth of a small vial, on to a 

 glass slide and is quickly examined under the microscope. If 

 oocysts are present, they will be found floating in the surface 

 layer. ' !f| 



"This method is advantageous in that a comparatively large 

 sample (0.77 of 2 cubic centimeters, or approximately 1.5 cubic 

 centimeters) is examined. Inasmuch as the sample is a composite 

 one, it is clearly much more representative of the total stool than 

 the sample used for simple smear examination. Comparative esti- 

 mates of the intensity of the infection, as judged by the numbers 

 of discharged oocysts, are possible because the samples are vol- 

 umetrically equivalent. Just how much more eflicient the D. C. F. 

 method is than the simple smear method has not been determined,^ 

 but on several occasions, oocysts were readily demonstrated by 

 the former method when long searching of smears from the same 

 material did not reveal any." 



Enmnerative Technique. The coccidial oocysts of most animals 

 are of sufficient size and resistance so that various methods de- 

 vised for the purpose of counting helminth ova may be applied 

 with only minor adaptations to the enumeration of coccidial 

 oocysts. Such techniques are very valuable in following the course 

 of experimental infections in actual quantitative terms of para- 

 site production, or in comparing various infections in terms of 

 oocysts discharged. 



The StoU dilution egg-counting method has l3een used for count- 

 ing coccidial oocysts from the cat and dog with very satisfactory 

 results. The original papers (Stoll, 1923, Stoll and Hausheer, 1926, 



* Hausheer and Herrick (1926) have shown that 500 hookworm eggs per 

 gram of stool must be present to insure a positive diagnosis by the smear 

 method, whereas as few as 20 per gram are always detected by the D. C. F. 

 method. 



