714 MEDICAL ENTOMOLOGY 



contents of the tube into a flat white dish, and dilute with water until the 

 solution becomes transparent ; when the specimen can be seen remove it 

 to clean water with a pipette or a brush. With carbol fuschin it is often 

 necessary to dilute the fluid to a considerable extent before the object 

 can be picked out, and it is therefore well to use as small a quantity of 

 the stain as possible. 



Many parts, such as whole heads of small flies, can be mounted in 

 hollow slides. When doing so care should be taken to place an excess 



of Canada balsam on the slide before lowering the 

 Mounting . . 



cover slip on to the specimen, or a bubble of air may 



get into the hollow, from which it is difficult to dislodge it. Instead of 

 using hollow slides, compression of the specimen may be avoided by 

 placing a fragment of a thin glass slide, a piece of cover slip, or a thin 

 capillary tube, beside it before lowering the cover slip. 



In making cleared preparations when material is abundant, a large 

 number of specimens should be placed in the solution at the same time, 

 and withdrawn at intervals, so that a series is obtained in which the 

 decolonisation has progressed to varying degrees ; these often present 

 strikingly different appearances. 



The dissection of fresh material is by far the most important method 

 of studying the anatomy, and gives more reliable information than can 



be obtained by sectioning the parts. When dealing 

 Dissection of fresh -., , ^, , . . , , ,, 



material wltn a P ar asitized arthropod, it is of the first impor- 



tance to evolve a sure and rapid method of dissection, 

 and when a large number of dissections of the same organ have to be 

 carried out, the method should be reduced to a routine, carried out with- 

 out deviation in every case. 



Dissecting needles as obtained from the instrument makers have too 

 coarse points for fine work, and they have to be ground down on a stone. 



Dissecting needles Tw kinds of blades are required, simple points and 

 lancet-like blades. If an emery wheel is available these 

 are easily made, but quite satisfactory instruments can be made with 

 an ordinary grind-stone and a soft razor stone. In making the lancet- 

 blades it is convenient to mark the flat side of the needle point by a 

 notch on the corresponding side of the handle. Only one edge should 

 be ground to a blade, or the needle will bend too easily. The needles 

 must always be finished off carefully on the soft stone, or a piece of 

 pumice soap, to get a smooth surface, otherwise the tissues will adhere to 

 them. The final polishing and sharpening should be controlled by 

 examination under the microscope. 



