294 RESEARCH IN PROTOZOOLOGY 



the bottom either further invaginated or blown out to adjust the 

 volume. 



A Lane tube (Fig. 19, B) is a cylindrical glass tube, closed and 

 flattened at one end. Its length overall is 125 millimeters and its 

 outside diameter is sixteen to seventeen millimeters. The upper 

 edge is ground perfectly plane, and may be cautiously heated in 

 a flame until the glass is just beginning to soften. The plane sur- 

 face must not be destroyed by the heating. This softening of the 

 edge prolongs the life and usefulness of the tube by preventing 

 the chipping at the top which readily occurs otherwise. The tube 

 is calibrated and etched to indicate fifteen cubic centimeters. 



The special centrifuge cup (Fig. 19, A) is best constructed 

 from a single piece of brass rod, bored and turned as illustrated. 

 This cup may be used with a standard four-place head on a hand 

 centrifuge. A heavy plating of nickel is a partial protection against 

 the corrosion from the salt water. 



Of the two methods of counting oocysts, Stoll's dilution method 

 is probably to be preferred, as it requires less apparatus to carry 

 out the procedure, and much less time to complete the determina- 

 tion. According to Hausheer, Herrick and Pearse (1926) the time 

 required to complete a Lane determination is from 109 to 125 

 minutes, whereas similar samples counted by the dilution method 

 (two slides counted) required from thirty to forty minutes. On the 

 other hand, the Lane method counts all of the oocysts in a meas- 

 ured quantity of stool and therefore is particularly useful in pick- 

 ing up light infections and in counting the first few and last few 

 oocysts of an experimental infection. When the infection is heavy, 

 it is almost futile to try to use the Lane method as the concentra- 

 tion of oocysts on the first few slides is so high. This difficulty 

 may be met by dilution of the sample, but in so doing the advan- 

 tage of counting the entire number of eggs is lost. 



In any method of counting oocysts it is necessary, as with hel- 

 minth ova, not to lose sight of the fact that the concentration of 

 oocysts must vary with the water content of the stool. Thus mushy, 

 or unformed stools contain more water and therefore a smaller 

 number of oocysts per unit volume or weight than feces which 

 are formed, but which are otherwise equivalent. Similarly, a diar- 

 rheic stool will be diluted, as regards oocyst content, even more 

 than a mushy one. Just what the ratio of dilution is under these 

 various conditions will probably have to be worked out for each 



