160 TWO NEW INSTRUMENTS FOR BIOLOGISTS, 



paralyzing solution such as chloral hydrate) in from two to three 

 hours, when they will be insensible and outstretched, and may be 

 fixed as desired. A specially large object-box is easily contrived 

 for larger specimens. 



If the objects to be treated are very minute, I now arrange the 

 oljject-box as illustrated in Fig. 4. Taking a piece of glass tubing, 

 whose external diameter is slightly less than the internal diameter 

 of the object-box, I cat therefrom two pieces, each about 5 mm. 

 long, and round oft' their sharp edges by heating. Call them 

 rammers. I then cut from the tinest linen some circular patches 

 having a diameter slightly gi*eater than the external diameter of 

 the object-box. Tlie next operation consists in taking one of the 

 rammers and with it forcing a wetted patch into one end of the 

 object-box. (Fig. 4, d, e.) To do this successfully, care should be 

 taken to arrange the patch concentrically on the end of the object- 

 box, and to place the rammer precisely upon the middle of the 

 patch. The patch is to be forced in only so far as is represented 

 in Fig. 4. The rammer may be allowed to remain in, or, if the 

 fit has been a snug one, may with safety be removed, the patch 

 remaining in place by virtue of its own elasticity ; the latter is 

 the preferable procedure. Join the object-box, open end upper- 

 most, to the filter, fill up with the fixation fluid, put in the objects, 

 and arrange the upper end of the box with a patch and the 

 I'emaining rammer. Bubbles must be avoided. The pieces of 

 linen give much less trouble in the end than plugs of cotton, in 

 which minute objects are liable to get lost. In this manner I have 

 treated such minute organisms as rotifers, paramaecium, &c., 

 without loss of specimens. The most delicate organisms return 

 fi'om this treatment in perfect condition. 



The flow from the capillary orifice of the filter is best regulated 

 by varying the inclination of the instrument. The flow is fastest 

 when the instrument hangs in a vertical position, and decreases as 

 the position of the instrument is made to approach the horizontal. 

 When the instrument is in a horizontal position there is no flow. 

 A convenient means of varying the inclination of the diflerentiator 



