METHOD OF FIXING THE SPECIMEN 719 



Malpighian tubes attached, a good deal of care is necessary in order to 

 preserve the desired arrangement of the parts. 



The preparation, when fixed to the coverslip, is treated as a film, and 

 is carried through graded alcohols to absolute alcohol, allowed to remain 

 in this for an hour or so, and then brought back to dilute alcohol of 

 approximately the same strength as the stain ; after staining and de- 

 colorization it is dehydrated and mounted in balsam on a slide in the 

 ordinary way. The whole operation can be performed without removing 

 the preparation from the original watch glass, the solutions being added 

 and withdrawn with a pipette ; square coverslips are more convenient to 

 work with than round ones, as it is easier to withdraw the solution 

 without touching the coverslip. 



The preparation may be fixed to a slide in the first instance, instead of 

 to a coverslip, and this is convenient when a series of staining jars with 

 graded alcohols, etc., are available ; but it should not be fixed to the 

 slide on which the dissection has been performed, as there is always 

 a certain amount of debris, ruptured fat cells, etc., on this, which take 

 on the stain later and obscure the specimen. Coverslips are on the 

 whole the most convenient and economical. 



This method is obviously capable of many modifications to suit parti- 

 cular purposes and circumstances. The following is the routine carried 

 out by the authors for ordinary work. 



Taking up the process at the point at which the saline has been remov- 

 ed as far as possible from the coverslip, a drop of Bless'* fluid is placed 

 on one side of the specimen, but not touching it, and the evaporation of 

 the saline watched under the dissecting microscope. When there is only 

 a thin film surrounding the tissue, the fixative is drawn towards the 

 specimen by means of a clean needle, and carried round the several 

 parts, such as the Malpighian tubes, the apical filaments of the ovaries, 

 etc., until they are all fixed to the glass. With a little practice this 

 can be done without any disturbance of the position of the parts. More 

 of the fixative is then added as the tissues become opaque, and finally 

 the coverslip is removed from the slide and inverted in a solid watch 

 glass of the fixative. A label is then attached (a slip of paper fastened 

 to the edge of the watch glass with a touch of Canada balsam), and the 

 watch glass covered up and sealed with vaseline. In half to one hour 



* The junior author is indebted to Dr. Ashworth for the following formula : 



Formalin ;, . 7 parts. 



Alcohol, seventy per cent . . 90 ,, 



Glacial acetic acid . . . . 3 ,, 



It should not be used more than ten days old. 



