840 SUMMARY OF CURRENT RESEARCHES RELATING TO 



when the treatment of the specimen with nitric acid is likely to 

 render subsequent staining by the ordinary means difficult. The 

 staining is effected by putting the colouring matters into the fluid 

 itself, adding the slightest trace of nitric acid, and leaving the pre- 

 paration to rest. Solution takes place, however, so slowly that it is 

 from twelve to twenty-four hours before the clear space round the 

 section appears. The pigment acts in this case like a staining material 

 introduced from without ; it disappears from those points where it 

 previously existed, and is precipitated in the nuclei, the other parts of 

 the tissue receiving only an insignificant amount. 



Seller's Imbedding Substance.* — Dr. C. Seller says that after 

 many experiments he has found pure paraffin two parts and rendered 

 mutton tallow one part, to be more satisfactory than any other 

 imbedding material in the majority of cases, because if poured into 

 the well of the microtome at a temperature of al)Out 120° it will not 

 shrink away when cooling, either from the tissue or from the wall of 

 the well. 



Strasser's Method of Imbedding.! — H. Strasser adds from 3 to 

 4 parts of tallow to the imbedding mixture recommended by 

 Kleinenberg (spermaceti 4 parts, castor-oil 1 part). In order to be 

 able to arrange very small objects in the required position and con- 

 veniently for cutting sections, he places them between plates of 

 mica in the warm mass, whose temperature must not exceed 45° C 

 After cooling, the laminae of mica may be readily detached, and the 

 mass containing the object in the required position, and forming a 

 thin plate, can then be fastened to a block of less easily melted 

 material by means of heated pins. 



Loewe's Modification of the Ranvier Microtome. J— Dr. L. Loewe 

 describes this as follows : — " The microtomes hitherto devised are 

 based upon two distinct principles. One of these is that of Verick 

 and Eivet, since variously modified by Brand, Leiser, Weigert, Long, 

 and others, leaving the general principle, however, unaltered. By 

 this instrument the preparation is raised on an inclined plane, as its 

 height is reduced by being cut away, the cutting knife always 

 remaining at the same level (see Fig. 195). 



" When the object is of small dimensions this instrument gives 

 results of great practical utility, and is certainly to be preferred to 

 free-hand cutting. But it is different when objects of large dimensions 

 and complex character have to be cut, such as the head of a full- 

 grown rabbit with skin and hair in a continuous series of frontal 

 sections, and it cannot be employed in any of those cases where 

 application of great force is required for dividing very hard parts, 

 teeth, bones, &c. This defect is inherent in the principle of the 

 apparatus, and cannot be obviated by any modification, however 



* ' Compendium of Microscopical Technology,' 1881, pp. 47-8. 



t Morphol. Jahrb., v. (1879) p. 243. Cf. Zool. Jahresber., i. (1880) p. 35. 



% ' Beitriige zur Aiiatomie iind zur Entwicklungsgeschichte des Nervensystems 

 dor Stliigethieic und des Meuacheu.' Cf. Zeitsclir. f. Mikr. ii, (1880) pp. 123-39 

 (5 fig«.)- 



