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SUMMARY OF CURRENT RESEARCHES RELATING TO 



latter : — The albumen and yolk of several hen's eggs is placed in a 

 porcelain mortar and well stirred, until it forms a thin yellow fluid, a 

 result generally obtained in a few minutes. This fluid is subsequently 

 passed through thin linen in order to remove the remaining mem- 

 branaceous fragments. The specimen previously hardened in alcohol 

 is then fixed by pins in a paper box, and covered with the fluid. The 

 preparation cannot, however, be immersed directly in alcohol for the 

 purpose of hardening. It must be first hardened by alcohol steam, taking 

 care never to raise the temperature of the steam above 30° C. For this 

 purpose Prof. Thoma uses a simple apparatus repiDsented in fig. 56. 

 A shallow water-bath a stands on an iron tripod h hh, and is 

 heated by a small flame c. The water- 

 bath is covered by a thin plate d d. Upon 

 this plate is a small glass vessel e, filled 

 with common alcohol and covered with a 

 perforated disk of tin //. On this disk 

 are placed the paper boxes g g, containing 

 the specimens and the imbedding fluid. 

 The latter and the alcohol vessel are again 

 separated from the external air by a glass 

 cover h. This apparatus slightly heated 

 will harden the imbedding masses within 

 a few days, after which time they are 

 removed and subsequently fully hardened 

 in a bottle containing ordinary alcohol. 

 The latter process determines the degree 

 of consistence of the imbedding mass. 

 It can be made extremely hard by re- 

 peated use of strong alcohol. After a few trials it will be easy to 

 find the convenient degree of consistence for each specimen. 



If the temperatxire of the alcohol steam is more elevated, it will 

 be found that the imbedding mass, instead of shrinking, will appear 

 to increase in volume, innumerable air-bubbles developing in the 

 emulsion. This can be easily avoided by using lower temperatures. 

 Another danger, however, exists in the holes which the pins make in 

 the walls of the paper boxes. The emulsion before hardening is so 

 very liquid, that it will pass through the smallest opening ; this 

 renders it necessary not to withdraw any of the pins from the sides 

 of the paper box, and to use boxes without any openings. It will be 

 found that this mass adapts itself perfectly to all surfaces of the 

 specimens without penetrating into their interior structure, and that it 

 can be cut aflmirably at all thicknesses down to ■ 003 mm. Another 

 very agreeable quality results from the fact that the newly prejiared 

 emulsion will adapt itself readily to hardened pieces. This enables 

 us to spread out fine membranes on pieces of the hardened imbedding 

 mass, and subsequently to imbed both in the way just described. 



After this praise of the egg-emulsion, it will be just to mention a 

 property which is occasionally disagreeable. It cannot be easily 

 detached from the sections, and we have no means of dissolving it in 

 media which do not injure the objects. The mass also colours in all 



Apparatus for hardening 

 egg-emulsion. 



