6fiS SUMMARY OF CURRENT RESEARCHES RELATING TO 



is laid on the surface of the scctiou is washed with spirit. lu practice 

 this docs not inv(dve any waste of time. These collodion sections may 

 bo mounted in glycerin or in balsam, in which latter case the uutlior 

 proceeds in two ways. First, when ho deals with sections of the blasto- 

 derm with an embryo up to the sixth day ; secondly, when the embryo 

 is larger and exceeds six days. 



(1) The embryos are hardened, stained, and kept in some provisional 

 medium. When required for sections they are passed through 3G' spirit, 

 absolute alcohol, the mixture of spirit and ether, very thin collodion, 

 and lastly the thick collodion. A piece of elder-pith cut straight is 

 washed with ether and then immersed in the thick collodion wherein 

 is the blastodermic disc. The latter is then placed on the pith in the 

 desired position and then carefully withdrawn, and after being allowed 

 to dry in the air for a minute or two is immersed in absolute alcohol 

 for at least 24 hours. The sections are then made, with or without 

 brushing the surface each time with collodion, and arc swept into water, 

 from which they are easily placed upon the slide in the proper order. 

 The sections are then dehydrated completely, and this done, the cover- 

 glass is imposed. Clarifying is then etfected by running benzine under 

 the cover-glass, and when this is complete the section is mounted in 

 balsam dissolved in benzine. The benzine and the benzine-balsam are 

 run under the cover-glass, and their entrance facilitated by drawing out 

 the fluid at the opposite side with filter-paper. The benzine used is 

 that known as benzine Collas. 



(2) If the embryo be too large to be stained en viasse, the section is 

 stained on the slide ; moreover, the largeness of the embryo necessitates 

 special care in the imbedding. They must be inclosed in a block of 

 collodion, and the hardening of a block requires that the evaporation 

 of the ether should be slow. This is effected by placing the cup in 

 which the embryo lies imbedded in thick collodion in a saucer con- 

 taining 36" spirit, and covering the two vessels with a bell-jar. In 

 12-36 hours the consistence of the mass is examined, and if the embryo 

 appear above the level, more thick collodion is added and the process 

 continued until the desired consistence is attained. The mass is then 

 dug out and cut into a block, which is stuck on elder-pith with collodion. 

 The sections must be stained on the slide, and this is done by coating 

 the sections with glycerin coloured with the staining solution (picro- 

 carmine, Grenacher, alum-carmine, &c.). Owing to the glycerin, there 

 is no fear that tlie section will dry : an aqueous solution may be used for 

 staining, but in this case the slide must be placed in a moist chamber. 

 In 24 hours the sections are well stained with carmine. The sections 

 are mounted in balsam, but, owing to their size, the beuzin and balsam 

 cannot be rim under the cover. The sections are fii'st dehydrated 

 with 36^ alcohol, the slide is then placed on a warm brick and washed 

 with absolute alcohol, then with bcnzin, and finally the balsam is 

 dropped or brushed on, and this followed by putting on the cover-glass. 



Schwabe's Sliding Microtome.* — Schwabe's microtome consists of 

 three separate parts ; an oblong support a (fig. 109) which also serves 

 for the slide-\\ ay, the piece h which carries the object, and the knife c. 



The slide-way c is grooved, and d flat ; in both cases ivory pegs are 

 used to prevent friction, these are shown at /, g, and h. The stability 



♦ Zeitschr. f. Wiss. Mikr., iv. (1887) pp. 463-4 (1 fig.)- 



