158 TWO NEW INSTRUMENTS FOR BIOLOGISTS, 



by meaus of caoutchouc tubing. The filter, c, is easily made as 

 follows : take a piece of glass tubing twice the length of the 

 required filter, heat it red hot, draw it out to arm's length and 

 break it in two in the middle ; remove all the capillary part except 

 about three inches on each half, heat, and bend into the required 

 form (c) ; next carefully heat the capillary portion near its 

 extremity in a small alcohol flame, draw out exceedingly fine and 

 break off so as to leave a minute orifice. All sharp edges should 

 be rounded off bv heatinor. 



To use the differentiator, proceed as follows. Suppose objects 

 fixed by corrosive sublimate are to be studied in balsam after 

 staining with borax-carmine. Fill the filter with perfectly clean 

 sublimate solution and insert a plug of cotton (previously boiled 

 in water to remove the air) at the u-bend (i; Fig. 3). Join the 

 object-box to the filter, fill up with sublimate solution, and push a 

 plug of cotton into the lower end of the box, avoiding bubbles. 

 Wrap the cotton in fine linen if the objects are minute. Put the 

 objects into the box, plug the upper end in the same manner as 

 the lower end, and finally join the box and filter thus filled to 

 the empty reservoir a, and hang the instrument up in the position 

 illustrated. The objects are now transferred to 33 per cent, 

 alcohol in the following manner : mix equal parts of sublimate 

 solution and 33 per cent, alcohol (call this mixture 2). Mix equal 

 parts of 2 and sublimate solution (call this 1). Mix equal parts 

 of 2 and 33 per cent, alcohol (call this 3). Add mixtui'e 1 to the 

 reservoir until it is one-fourth full, mixture 2 until it is half full, 

 mixture 3 until it is three-fourths full, and then fill up with 33 

 per cent, alcohol. If the successive mixtures are added with 

 sutficient care, they will, owing to difference in specific gravity, 

 remain distinct. If forced rapidly in, a nearly uniform mixture 

 of about equal parts sublimate solution and 33 per cent, alcohol 

 will result. The desirable procedure lies between these two suppo- 

 sitions, and gives rise to a uniform gradation or differentiation 

 from sublimate solution to 33 per cent. al/:ohol in passing ujywards 

 through the reservoir. A good procedure which always .secures this 

 result is to add the successive fluids carefully and then to dance 



