718 MEDICAL ENTOMOLOGY 



deal with them at leisure and can also use the camera lucida more effect- 

 ively. The following method is a modification of that taught to one of 

 the authors by Dr. Ashworth. 



The part to be mounted is dissected in saline in the ordinary way, 

 special care being taken to free it from fat body and other debris, and is 

 severed from the rest of the material. It has now to be transferred to 

 a coverslip, and arranged in such a manner as to best display the anatomy. 

 If the part is large, it may be lifted up on the point of a clean needle, 

 and placed in a drop of saline on the coverslip. If a dirty needle, or one 

 with a rough edge, is used, trie soft tissue will stick to it, and it may be 

 impossible to detach it. A better plan is to flood the whole slide with 

 saline, remove everything except the part required, and place a coverslip 

 beside it. With an excess of saline it is easy to move the prepara- 

 tion to the coverslip. Then drain off the saline with a pipette and filter 

 paper, and arrange the parts as required ; the coverslip will adhere to the 

 slide sufficiently well to allow of the necessary manipulation on account 

 of the moisture between the two. 



The next step is the one on which the success of the whole process 

 depends. It is necessary to fix the specimen to the coverslip in such 



a wav that no part of it will become detached during 

 Fixation , . 



the subsequent manipulations, and, as this must be 



done with a rapidly acting fixative, there is always the risk that 

 the surface tension between the saline solution and the fixative will 

 be enough to either float off the specimen or to disturb the desired 

 arrangement. The important point is to get rid of as much of the 

 saline solution as possible without allowing the tissues to become 

 dry. First remove the excess of moisture with fine points of filter 

 paper, while holding the slide under a low magnification. When 

 this has been done the coverslip should be removed from the slide by 

 pushing it towards the edge, and held between the finger and thumb. 

 When the preparation is just on the point of becoming dry, allow a small 

 drop of the fixative to flow from the edge of the slide towards the speci- 

 men. The part which it meets will possibly move a little, but in a second 

 or two it will adhere to the glass, and as the alcoholic solution drives the 

 watery saline in front of it, the whole preparation will become opaque and 

 at the same time adherent to the glass. As soon as this has occurred 

 cautiously flood the whole of the coverslip and at once immerse it, face 

 downwards, in a watch glass of the fixative. With simple objects, such 

 as the mid-gut only, or with salivary glands, the fixation is of course 

 quite easy to carry out, but with dissections of the whole gut, with the 



