f,20 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



of a U, the two ends only just projecting beyond the edge of the slide. 

 The other slide is laid on top, and the pair are secured by means of 

 rubber bands. This arrangement constitutes the U-cell. It is filled by 

 standing it in a nearly vertical position, and then injecting the fluid 

 containing the organisms with a pipette through the open end of the U. 

 Or it may be filled by siphoning by means of a piece of woollen yarn 

 thrust through the U-aperture to a depth of 5-10 mm. 



The U-cell may also be used for a circulating medium, as shown in 

 fig. 124. The cells are placed at an angle in a glass dish, and lean 

 against an inner vessel placed in the centre of the first. The dimen- 

 sions of the two vessels should be so selected that the upper ends of the 



Fig. 124. 



cells come in contact with the inner vessel at about 5 mm. below its 

 upper end. From the inner vessel water is led by cotton-yarn siphons 

 S" into the cells. A constant-level siphon S' is hung over the wall of 

 the outer vessel. The inner vessel is supplied from a bottle fitted with 

 an air-tube A and a siphon-tube S. The inner vessel and its yarn- 

 siphons should be protected from dust by a glass plate, the edge of which 

 is notched to admit the siphon-tube. Woollen yarn is used when a 

 rapid flow is desired, cotton for a slower rate. 



In the preparation of microscopical specimens requiring change of 

 fluids under the cover-glass, the author uses cotton- wool. A small 

 quantity of dry absorbent wool is placed on a slide and moistened with 



