ZOOLOGY AND BOTANY, MICBOSCOPY, ETC. 443 



plan of section. In order to fix the egg in any given position in the 

 imbedding mass, Hertwig proceeds as follows: — 



a. A small block of the hardened mass is washed in water to 

 remove the alcohol, and in the upper surface of the block, which has 

 been freed from water by the aid of filtering paper, a small hollow is 

 made. This hollow is then wet with the freshly-prepared fluid 

 mass. 



h. The egg is washed in water to remove the alcohol, placed on a 

 piece of fi.ltering paper to get rid of the water, turned on the paper by 

 a fine hair brush until it has the position desired ; the point of the 

 brush is next moistened and pressed gently on the upper surface of 

 the egg ; the egg adheres to the brush, and may thus be transported 

 to the hollow prepared for it in the block. 



c. After the egg has thus been placed in position, a drop of abso- 

 lute alcohol carefully applied will coagulate the " fluid mass " with 

 which the hollow was wet, and thus fix the egg to the block. The 

 block is again washed, and finally imbedded in the egg-mass, which is 

 prepared in the following manner.* 



The white of several eggs is separated from the yolk, freed from 

 the chalazae, cut with shears, and thoroughly mixed by shaking with 

 a 10 per cent, solution of carbonate of sodium (15 parts of the white 

 to 1 part of the solution). The yolk is next added, and the mixture 

 shaken vigorously. After removing the foam and floating pieces of 

 yolk by the aid of filtering paper, the so-called " egg-mass " is ready 

 for use. It is this fluid with which the hollow in the solid block is 

 wet, as before mentioned, the block itself being only a piece of the 

 same mixture after it has been hardened in alcohol. 



Calberla soaks the egg a few minutes (5-20) in the fresh white of 

 the egg before imbedding. Hertwig appears to omit this part of the 

 process. 



After the egg has been fixed to the block as before indicated (c), 

 it is placed in a paper box and covered with the fresh mass (1-2 cm. 

 deep). The box is then placed in a vessel that contains alcohol 

 (75-80 per cent.), enough to bathe its lower half; the vessel, covered 

 with a funnel, is heated over a water-bath for 30-40 minutes, care 

 being taken not to hoil the alcohol. The imbedding substance, thus 

 hardened, is next placed in cold alcohol (90 per cent.), which should 

 be changed once or twice during the first twenty-four hours. After 

 remaining in alcohol for about forty-eight hours, the imbedded egg is 

 ready for cutting. 



Preparing Sections of and Examining Embryos.t — The second 

 edition of Foster and Balfour's ' Elements of Embryology ' contains 

 an Appendix, in which are given some very succinct directions for 

 preparing sections of the embryo of the chick, divided into three heads : 

 — (1) Hardening (picric acid, corrosive sublimate, osmic acid, chromic 

 acid, and alcohol) ; (2) Staining (hematoxylin, borax-carmine, car- 

 mine, picro-carmine, and alum-carmine) ; (3) Imbedding (in paraffin) ; 



* Calberla's method of imbeddiug. Morph. Jahrb., xi. (1876) p. 445. 



t Foster and Balfour'a ' Elements of Embryology,' 2nd ed. (1883) pp. 423-70. 



