292 RESEARCH IN PROTOZOOLOGY 



sticks. Diarrheic stools may be handled with either wooden or 

 cardboard "ice-cream spoons." The advantage of these instruments 

 over the metal spatula or spoon is that they do not have to be 

 cleaned and dried for each specimen but can be discarded with 

 each stool, and a fresh set known to be clean, dry, and uncon- 

 taminated may be used for the next. The flask is filled with water 

 to the calibration mark, and two or three cubic centimeters of 

 mixed medium and small lead shot are added. The flask is shaken 

 until the contents are uniformly dispersed, and immediately after 

 shaking (before the oocysts have time to settle out), a sample is 

 poured into a "Lane tube" (to be described) up to the fifteen cubic 

 centimeter calibration mark. The tube is placed within the special 

 centrifuge cup (to be described) which is placed in either a special 

 Lane centrifuge or in an ordinary hand centrifuge and is whirled 

 at a speed of looo revolutions per minute for two minutes. The 

 Lane tube is withdrawn and the contents (known as the "pour- 

 off") are carefully decanted into another Lane tube, care being 

 taken to retain all of the sediment within the original tube. A 

 boiled saturated solution of common salt is added, a little at a 

 time, shaking the tube gently between additions so that the sedi- 

 ment will be suspended without bubble formation, until the tube 

 is nearly filled. It is placed in the special cup, and saturated saline 

 is added with a pipette until the surface level of the solution is 

 even with the ground edge of the tube. A thick coverglass 

 (i8 X i8 millimeters, No. 3) is laid upon the mouth of the tube 

 between the four horns of the cup so that the horns are opposite 

 the middle of the sides of the coverslip. A small piece of paper 

 (about fifteen millimeters square) is dropped on to the coverslip. 

 The entire centrifuge cup and contents is lifted from the centri- 

 fuge, and, with the forefinger placed against the paper on the 

 coverslip, is inverted several times, being careful not to spill any 

 of the contents. The cup and tube are replaced in the centrifuge, 

 and are rotated for one minute at 1000 revolutions per minute. 

 The coverslip is removed by firmly grasping it at the corners with 

 the thumb and forefinger and suddenly raising it. It is then 

 mounted on a slide, wet side down, and the oocysts are counted 

 immediately. The tube is again filled with saturated saline, cov- 

 ered with a fresh coverslip and is manipulated as before. The pro- 

 cedure is "pushed to finality," i.e., coverslip preparations are made 

 until two consecutive preparations are negative. For very accurate 



