ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



881 



Fig. 1G2. 



piece of metal has the form of a carpenter's square, with the end of 

 the shorter arm triangularly enlarged outward. A convenient size will 

 be found in pieces measuring 7 cm. (long arm) by 3 cm. (short arm), 

 and 7 mm. high. With such pieces a hox may be constructed at any 

 moment by simply placing them together on a round plate of glass, 

 which has previously been wet with glycerine and gently warmed. 

 The area of the box will evidently vary according to the position 

 given to the pieces, but the height can be varied only by using 

 different sets of pieces. In such a box the paraffin may be kept in a 

 liquid state by warming now and then over a spirit-lamp, and small 

 objects be placed in any desired position under the Microscope. 



It is well to imbed in a thin layer of paraffin, so that the object, 

 after cooling, may be cut out in small cubical 

 blocks, which may be easily fixed, for cutting, 

 to a larger block of hard paraffin. 



Only in the case of very delicate objects 

 is imbedding in wax and oil after Briicke's 

 plan to be preferred. White of egg has not 

 proved as permanent as might be desired. 

 Gelatine is a convenient imbedding medium, 

 and Dr. Mayer has devised a process by 

 which it is deprived of its elasticity. It is 

 allowed to soak as usual in water, then heated 

 and I to ^ a volume of castor oil added, shaken 

 well, and shortly before getting cold pour 

 the mixture into a bowl. When afterwards 

 all the castor oil has been extracted by 90 per 

 cent, alcohol the gelatine remains as a fine 

 porous matter, a sort of artificial pith, and 

 is at once ready for use. It must not of 

 course be exposed too long to the air as this 

 would soften it. Under the Microscope this 

 form of gelatine is less troublesome than lilac 

 pith and has the advantage that it can be produced in any size and 

 always even. 



VII. Cutting. — Objects are cut dry with a microtome, and the 

 rolling of the sections may be prevented by holding a thin narrow 

 spatula over the edge of the knife while cutting. The spatula may 

 be made of brass, or of paper fastened to a flattened needle. The 

 spatula should be bent slightly, and the convex face held over the 

 paraffin without pressure. A small brush, slightly flattened, is used 

 for the same purpose in Leipzig. 



Andres' Methods of treating Actiniae.* — Among the various 

 methods employed by Dr. Andres in killing the Actinia?, the three 

 following, given in the order of their excellence, are said to have 

 worked most satisfactorily : — 



A. Corrosive sublimate. — With small animals a hot solution, used 

 in the manner recommended by Dr. Lang, gives good results ; with 



* Atti R. Accad. Lincei, v. (1880) p. 9. 



