SYRTJP AND GUM CONGELATION MASS. 1C9 



305. Weil's Canada Balsam Method (Zeit.f. wiss. MiJc., v., 2, 1888, 

 p. 200). Balsam heated till brittle when cold, then dissolved in chloroform. 

 Heat the objects in the mass on a water-bath. For further details, see 

 Journ. Roy. Mic. Soc., 1888, p. 1042. 



White of egg Masses. 



306. 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 considered to 

 be entirely superseded. See Zeit. f. wiss. Mik., 1884, p. 223 (RUNGE) ; 

 Morph. Jahrb., Bd. ii, 3tes Heft, 1876, p. 445 (CALBERLA) ; Zool Anz., 6, 

 vol. i, 1878, p. 130 (SELENKA) ; Journ. Roy. Mic. Soc., 1883, p. 304 

 (THOMA), and BECKER'S Zur. Anat. d. ges. u. Ttrariken Linse (RUGE). 



Congelation Masses. 



307. 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. 



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

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

 (of hardened brain) in a Kutherford'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. 



