538 



SUMMARY OP CURRENT RESEARCHES RELATING TO 



The apparatus (fig. 109) is on the principle of a dialyser, and 

 consists of a broad glass tube with a projecting upper rim (like that 

 of a hat), and with a paper membrane at the lower end. This is 

 inserted in a larger vessel with a broad rim at the neck. The two 

 rims fit together closely, and seal the larger vessel. The latter is 



Fig. 109. 



filled to a convenient level with absolute alcohol, the smaller contains 

 the object with a little of the weak alcohol in which it previously lay. 

 A gradual diffusion occurs and a very perfect dehydration is rapidly 

 effected. The process may be made more gradual by the use of a 

 double tube, the outer containing weaker alcohol. At the foot of the 

 large vessel is a layer of burnt sulphate of copper which prevents the 

 dilution of the absolute alcohol. The dehydration of the inner tube 

 containing the object may be conveniently tested (after twenty-four 

 hours or so) by removing a little of the fluid in a pointed pipette, and 

 allowing a drop to pass slowly into a test-tube with 98° alcohol. If 

 the fluid be absolute alcohol, a small portion from the pipette will 

 be detected passing upwards, or downwards if the fluid be below 98°. 



Prof. Schulze also describes a modification of a method of securing 

 the safe preparation of delicate objects by allowing them to sink 

 through layers of different fluids. In his improved form a closed 

 tube contains an inferior layer of Canada balsam, above that 3 c.cm. of 

 xylol, and uppermost 1 c.cm. of absolute alcohol. At the level of the 

 Canada balsam there is a cock for allowing the upper layers to flow 

 off, after which the object is removed from the Canada balsam into 

 which it has sunk. 



Efficiency of the Micrometer-screw.* — Herr J. Ost discusses the 

 action of the micrometer-screw as used in microtomes, and endeavours 



* Zeitschr. f. Wiss. Mikr., ii. n885) pp. 29.5-300. 



