xxii INTRODUCTION. 



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 tubes is, that the idea of applying the mouth to the end of the tube which 

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



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

 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 hah* 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 4 inches in length at least ; the spring- (separating-) action shonld 

 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 at- 

 tention 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 " tenaculum- 

 forceps" are very useful occasionally in injecting. These forceps lock by 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 be- 

 tween the ends of these 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 indispensable to the 

 injector. They should be short and not heavy, otherwise the vessel may be torn by their 

 weight. , 



Surgical " dressing forceps " are also frequently of use ; and long " oesophagus forceps " 

 with scissor handles are serviceable for removing portions of plants, &c. from large jars or 

 glass vessels. 



Needles. For separating the parts of minute objects, fine points are requisite ; these are 

 found in common needles of moderate size fixed by one end into the handle of a water- 

 colour brush. These are easily prepared : the needle is cut in half by cutting pliers ; the 

 blunt end is then forced into the stick, about half an inch in length being left projecting. 

 Surgeons' " cataract needles " ground down are elegant instruments of this kind, but they 

 require to be shortened. For minute dissection of plants, all needles require pointing on a 

 hone. 



A stout sable-hair or fine bristle, inserted into a slender wooden handle, is frequently of 

 use in isolating minute bodies, as Diatomaceae, which would be broken by any other instru- 

 ment. It is used thus : suppose we have a number of Naviculae, or the like, in a bottle, 

 mixed with other bodies, and we wish to isolate one for preservation. A small quantity of 

 the deposit is taken up with a dipping-tube, and allowed to escape upon a slide in such 

 manner as to form a narrow stripe upon it. This is then examined with the lowest power 

 with which the object can be distinguished, and one near the margin of the liquid stripe is 



