4 CHAPTER I. 



In dealing with^extremely delicate objects, it may be necessary to take 

 special precautions in order to avoid injury to them through the violent 

 diffusion-currents that are set up in the passage from water to alcohol, or 

 from one bath of alcohol to another of considerably different density. Some 

 kind of diffusion-apparatus may conveniently be used in these cases. The 

 objects may be placed with some of their liquid in a tube plugged at one 

 end and closed at the other by a diaphragm of chamois skin or other suitable 

 membrane, the tube being then immersed in a vessel containing the grade 

 of alcohol that it is desired to add to the liquid in the tube, and the whole 

 allowed to remain until by diffusion through the diaphragm the two liquids 

 have become of equal density. Or COBB'S differentiator (Proc. Linn. Soc., 

 N.S.W., v, 1890, p. 157 ; Journ. Roy. Mic. Soc., 1890, p. 821) may be 

 employed. Or, more conveniently in most cases, the apparatus described 

 and figured by HASWELL (Proc. Linn. Soc., N.S.W., vi, 1891, p. 433 ; 

 Journ. Roy. Mic. Soc., 1892, p. 696). This consists of two wash-bottles 

 connected in the usual way by tubing, and furnished, the one with an over- 

 flow-tube, and the other with a feeding-tube leading from an elevated 

 reservoir connected with it by means of a regulating tap or drop arrange- 

 ment. The objects are placed in the first bottle ; some of the same liquid 

 as that containing the objects is placed in the second bottle ; and alcohol of 

 the grade that it is desired to add is led into it from the reservoir. The 

 mixture of liquids therefore takes place in the bottle that does not contain 

 the objects, and the mixture itself is gradually led over to the objects 

 through the siphon-tube connecting the two bottles. Another apparatus 

 for rapid dehydration, devised by CHEATLE, will be found described in 

 Journ. Pathol. and Bacteriol., i, 1892, p. 253, or Journ. Roy. Mic. Soc., 

 1892, p. 892. It is hardly simple enough to be recommendable. 



A capillary siphon for the aspiration of liquids in the 

 fixing, staining, and washing of suspended blood-corpuscles, 

 sperm-cells, protozoa, and the like, is described by EWALD, 

 in Zeit. BioL, Bd. xxxiv, 1897, p. 253. 



I would here call attention to the varied usefulness of the " Siebdosen " 

 or sieve-dishes of STEINACH, ZIMMEEMANN, and SUCHANNEK (vide Zeit. f. 

 wiss. Mik., iv, 4, 1887, p. 433, and vii, 2, 1890, p. 158). They consist of a 

 covered glass capsule into which is fitted a " sieve " made of a watch-glass 

 pierced with holes and supported on legs, and are very handy, not only for 

 staining, washing out, treatment with vapours, etc., but for any operation 

 in which it is desirable to have specimens supported in the upper layers of 

 a quantity of reagent. They are sent out in a very neat form by Griibler 

 and Co. FAIECHILD'S perforated porcelain cylinders for washing (Zeit. f. 

 wiss. Mik., xii, 3, 1896, p. 301) seem to be a very neat idea. These are 

 made small enough to be floated by the cork that closes them. See also 

 EWALD'S section-washing apparatus (Zeit. BioL, Bd. xxxiv, 1897, p. 264). 



It is sometimes stated that it is necessary that the last alcohol-bath 

 should consist of absolute alcohol. This, however, is incorrect, a strength 

 of 90 per cent., or at all events 95 per cent., being sufficient in most cases. 

 For the small amount of water that remains in the tissues after treatment 

 with these grades of alcohol is efficiently removed in the bath of clearing 



