IMBEDDING 11 



157. Handling and Imbedding Very Small Objects. When 

 dealing with ova of many marine invertebrates, the ovaries of 

 DrosophilcTi, and other small objects, much time and valuable 

 material is saved if they are enclosed, in some way, so as to 

 prevent loss during dehydration and imbedding. In this section 

 are brought together some of the devices with which we are 

 familiar, but in several instances we are unable to cite the 

 originator of the method. 



After any fixation which requires washing in running water, 

 Painter's method is to place the material in a short piece of glass 

 tubing bent into the form of a J. The diameter of the tubing 

 should be large, say 6 to 10 mm. The tube is placed upright in 

 a small glass dish and water is dropped into the long arm, by a 

 capillary syphon. Should any of the material be washed out of 

 the tube it will be caught by the glass dish in which the tube is 

 placed. This method works well with ovaries of Drosophilae. 



After fixation and washing, small objects can be mixed in a 

 drop or two of white of egg. With a scalpel, the mass is scraped 

 off on to the edge of a slip of paper and the albumen coagulated 

 in 70 per cent, alcohol, or a 5 per cent, solution of corrosive 

 sublimate, or a 2 per cent, solution of chromic acid. The choice 

 will dei^end on the method of preservation used in the first place. 

 The paper slip, which can be labelled, serves as a convenient handle 

 and need not be detached until the material is actually imbedded. 



In America it is a common practice to employ the inner skin 

 from a Drosophila pupa as a container for small objects which 

 are to be imbedded and sectioned. Lying just beneath the hard 

 outer pupal case, in Drosojjhila species, there is a thin membrane 

 surrounding the pupa which can be easily removed with needles 

 a day or two before the adult emerges. The skin which surrounds 

 the abdomen and which will usually come off intact, is the part 

 used as a case into which ovaries and like material can be pushed 

 with the aid of a blunt curved needle under a dissecting micro- 

 scope. Painter has found it desirable to insert into the pupal 

 skin a blunt curved needle and straighten out the wall, immediately 

 after removal from the pupa and then to transfer the skin on the 

 needle to 50 or 70 per cent, alcohol. This causes the skin to 

 harden somewhat and is a convenient method of storing the cases. 

 In use, it is better to place the ovaries in the pupal skin just after 

 washing or while they are in .35 per cent, alcohol, because in higher 

 alcohols they become friable and crush easily. The skin contain- 

 ing the ovaries may now be passed through the higher alcohols, 

 stained with eosin, if desired, and cleared and imbedded in the 

 usual way. 



When a considerable amount of material is available it can be 

 drawn into a pipette and placed in the niiddle of a piece of more or 

 less rectangular shaped membrane, such as the skin shed by many 



