FREEZING MASSES. 207 



White of Egg Masses. 



314. The White of Egg Method consists in imbedding in a white of 

 egg emulsion, and hardening by alcohol or by the combined action of alcohol 

 and heat. The method had certainly a raison d'etre at one time, as 

 giving results which could not then be obtained by other means. But the 

 method was extremely cumbrous, had many defects, and must now be con- 

 sidered to be entirely superseded. See Zeit. f. wiss. Mik., 1884, p. 223. 

 (EFNGE) ; Morph. Jahrb., Bd. ii, 3tes Heft, 1876, p. 445 (CALBEELA) ; 

 Zool Anz., 6, vol. i, 1878, p. 130 (SELENKA) ; Journ. Roy. Mic. Soc., 1883, 

 p. 304 (THOMA) ; and BECKER'S ZurAnat. d. ges. u. kranJcen 



Congelation Masses. 



315. The Freezing Method. Fresh tissues may be, and are, 

 frequently frozen without being included in any mass, and in 

 certain cases very satisfactory sections can be obtained in this 

 manner. But the formation of ice crystals frequently causes 

 tearing of delicate elements, and it is better to infiltrate the 

 tissues with a mass that does not crystallise in the freezing 

 mixture, but becomes hard and tough. Gum arabic affords 

 such a mass. Some workers use common gum water, which 

 is either poured into the well of the microtome or round the 

 object on the object plate, according to the form of microtome 

 used. 



316. Syrup and Gum Congelation Mass (HAMILTON, Journ. of 

 Anat. and Phys., xii, 1878, p. 254). Hamilton cuts sections 

 (of hardened brain) in a Rutherford's freezing microtome. 

 The hardening reagent having been soaked out by water, the 

 tissues are prepared for freezing in the following manner, 

 which it is important to observe, otherwise it will be found 

 that the crystals of ice so break up the delicate nervous tissue 

 as to render it totally useless for minute examination. The 

 tissues are to be well soaked in syrup. The sugar somewhat 

 retards the freezing, and besides, seems to alter the manner 

 of crystallisation, so that instead of the ice being spicular in 

 form it becomes granular, and does no injury to the parts. 



The syrup requires to be of a particular strength, viz. double 

 refined sugar, 2 ounces ; water, 1 fluid ounce. 



Wash the superfluous syrup from the surface, and put into 

 the ordinary mucilage for an hour or so before cutting. Imbed 

 in the freezing microtome with mucilage in the usual way. 

 Float the sections into water. 



