DIPPING-TUBES-FORCEPS. xxv 



hand, and rubbing the surfaces with, a fold of a cloth, leather, or silk handkerchief covering 

 the same parts of the right hand. But the thinnest glass cannot be wiped in this way 

 without being broken. This requires to be held at the edge by the finger and thumb of 

 the left hand applied to the flat surfaces, and to be drawn slowly through the fold of the 

 cloth in the hand. A very thin layer of mica is useful as a cover with the highest powers, 

 as it prevents the risk of scratching the object-glass, the lower surface of which is often 

 flush with the edge of the brass mounting. 



Dipping-tubes. These are glass tubes varying in length from about 5 inches to a foot, 

 and in calibre from to an inch. They are cut of the proper length by a three-square file, 

 and the ends gently fused in the flame of a spirit-lamp. One end is then coated outside 

 with sealing-wax and spirit, or some other coloured liquid, so that the same end may always 

 be used for the same purpose. They are of use for removing objects from water or other 

 liquids in which they may be contained. Suppose, for instance, it is required to examine 

 some deposit lying at the bottom of a liquid, or an object suspended : the fore finger of the 

 hand in which the tube is held is placed upon the upper end of the tube so as to close it ; 

 the other end is then immersed in the liquid and brought into contact with, or as near as 

 possible to the object, and the finger removed from the upper end. Hydrostatic pressure 

 then forces the liquid, and with it the object, into the lower part of the tube, and it can 

 be transferred to a slide. When a tube of narrow calibre is used, the liquid and object 

 are retained within the tube by capillary attraction ; they must then be removed by 

 gently blowing at the upper end, the lower end being placed upon the slide. The use 

 of colouring one end of the tube is, that the application of the mouth to the end of the 

 tube which has been immersed in some offensive liquid, as foetid water, &c., may be 

 avoided. 



These tubes should be kept in a glass of distilled water, with the coloured ends 

 uppermost. 



When a large tube is used, as in removing the larva of an insect, a tadpole, c., the 

 quantity of liquid removed is also large, and will be more than is required on the slide. 

 The tube should then be emptied into a watch-glass, and the object placed upon the slide 

 or in the live-box by a camel's-hair pencil. 



Forceps are in constant requisition for taking hold of minute objects, dissecting, &c. 

 Those used for medical purposes (common steel dissecting or surgical forceps) are best. 

 There are three points to be attended to in the selection of them. They should not be too 

 short, i. e. less than four inches in length at least ; the spring- (separating-) action should 

 be very feeble ; and the points should be perfectly flat and smooth where they come into 

 contact. If forceps are shorter than the above length, they are not easily held steadily : 

 if the spring-action be strong, on holding an object, as in dissection, with the forceps, the 

 attention being perhaps directed to the scalpel, needle-points, &c., the blades of the 

 forceps separate, and the object escapes from their grasp. If the forceps have teeth or 

 are grooved, perhaps after laying an object out upon a slide under water, or elsewhere, a 

 portion of it becomes entangled in the teeth, and the whole displaced. Surgical " tena- 

 culum-forceps " are very useful occasionally in injecting. These forceps lock bv their own 

 spring-action. Supposing, then, the injection is escaping from the orifice of some vessel 

 which has been overlooked and no assistant is at hand, on including the open end of the 

 vessel between the ends of those forceps, which may then be left hanging, it is firmly 

 fixed, and the operator has both hands disengaged to tie it ; in fact, these forceps are 



