WITH THE MICROSCOPE. 85 



to have a ridge around the glass tube, about three inches from its 

 upper extremity, pi. XXII, fig. 140. 



159. Removing the Deposit with the Pipette. The removal of 

 the deposit is easily effected. The pipette is held by the middle 

 finger and thumb, while the index finger is firmly applied to its 

 upper extremity. The point is next plunged beneath the surface of the 

 fluid and carried down to the deposit, a portion of which will rush 

 up the tube if the pressure of the finger upon the upper extremity be 

 slightly diminished. The deposit having entered the tube, the pres- 

 sure is re-applied, and the deposit contained in the pipette can be 

 removed from the fluid, fig. 141. 



ICO. On Separating the Coarse from the Finer Particles of a 

 Deposit. Many deposits, by being diffused through a large quantity 

 of water, may be divided into several portions. The fluid, with sub- 

 stances suspended in it, is well stirred, and, after being allowed to 

 stand for a very short time, all but the deposit is poured off into 

 another vessel. In this the fluid is again allowed to stand for a short 

 time, and again poured off. This process may be repeated several 

 times. In the first glass, only the coarser particles will be found ; 

 in the second, slightly finer particles ; in the third, still finer ones, 

 and so on ; a longer period being allowed for the subsidence in each 

 successive case. 



The coarse particles may also often be separated from finer ones 

 by straining the deposit through muslin. Various preservative solu- 

 tions, which I have already described, are applicable for preserving 

 deposits from fluids. Many, again, may be mounted in Canada 

 balsam. 



161. Separation of Deposit when very small in Quantity. Where 

 the deposit is exceedingly small in quantity, and diffused through a 

 great bulk of fluid, a slight modification of the above plan must be 

 resorted to. The pipette, containing as much of the deposit as can 

 be obtained, is removed from the glass vessel containing the fluid. 

 Its contents are prevented from escaping by the application of the 

 finger to its lower orifice. The upper extremity is then occluded 

 with a small cork. Upon now removing the finger from the lower 

 orifice, of course no fluid will escape. The pipette is allowed to 

 stand with its mouth downwards upon the glass slide, in which 

 position it may be permitted to remain some hours, either being 

 suspended with a string or allowed to lean against some upright 

 object. It is obvious that under these circumstances the most 

 minute deposit contained in the fluid will gravitate to its lower part, 

 and be received upon the slide, without the escape of much of the 

 fluid, fig. 145, pi. XXII. Or the sediment, having been allowed to 



