and Laboratory Methods 



2081 



Fig. 4. 



them from a pipette into the groove, where, owing to the confined space, they 

 will remain close together. The bottom of the dish is then rapidly cooled on 

 the surface of water, and, when the paraffin is thoroughly hardened, it may 

 be removed without diflficulty. The objects are held in the portion of the 

 paraffin which previously filled the groove, and which 

 now projects from the surface of the block. With a 

 little trimming the paraffin is ready for sectioning. 



The dish is 4(» mm. square and mm. high; the 

 diameter of the concavity is 34 mm. and its greatest 

 depth 4^2 miiti- The groove, which is slightly beveled 

 at the ends, is 11 mm. long on the bottom, 'J. mm. 

 wide, and '1 mm. deep. In Fig. '2 is shown a section 

 of the glass through the long axis of the groove, and 

 in Fig. 3 a section taken across the groove. When 

 the hardened paraffin is removed from the dish it has the form seen in Fig. 4; 

 the embedded objects are indicated at a. The block, when trimmed and ready 

 for sectioning, may be cemented to a piece of wood or to the metal paraffin- 

 holder of the Minot microtome. (Fig. 5.) 



I have thoroughly tested the practical usefulness of this dish, and my experi- 

 ence has shown that it may be manipulated so easily and conveniently that the 

 embedding in it of such minute objects as it is intended for becomes as simple 

 an operation as the embedding of larger ones which maybe handled individually. 

 The method of procedure which I have used is as follows : The objects are 

 dehydrated in the usual manner in round-bottomed tubes, the change of liquids 

 being made entirely by means of a pipette. After saturation with the solvent, 

 the tube is placed on the paraftin-bath and melted paraf- 

 fin added with a warm pipe'tte. When ready for embedding, 

 the objects are drawn into a pipette and carefully dropped 

 into the groove of the watch-glass containing melted 

 paraffin. A very /////t' i/i/ufe glycerine must be previously 

 rubbed on the inside of the dish, and also on the sides 

 and bottom of the groove, to prevent the tendency of the 

 paraffin to stick to the glass. If any of the objects 

 should have failed to fall into the groove when dropped 

 from the pipette, they may be readily pushed in with 

 a needle or small spatula ; or if the number of objects is not great, and they 

 should scatter along the bottom of the groove, they may be pushed to one 

 end in the same way. I also find that it is possible to dispense entirely with 

 the round-bottomed tubes, as the whole process may be performed in the dish by 

 keeping the objects in the groove and making the change of liquids with a pipette. 

 The dish is now cooled rapidly on the surface of water, and when the paraffin 

 is thoroughly hardened, a knife edge is inserted under the paraffin opposite one 

 end of the groove and the entire mass lifted up. The projection of the paraffin- 

 mass containing the embedded objects may be sectioned with the edge of the 

 microtome knife set either parallel to its long axis or perpendicular to it, as may 

 be desired. In either case the front and back edges of the mass are already 

 parallel, and need no trimming before sectioning. 



In addition to its use in embedding large numbers of loose, minute objects, 

 the dish is serviceable for the purpose of orientation. A small object lying in 

 the groove may be rapidly oriented with a warm needle under the microscope, 

 and placed in any desired position. It is possible then to cool the dish without 

 disturbing the object. George Lefevre. 



Zoological Laboratory, University of Missouri. 



