204 COLLODION AND OTHER IMBEDDING METHODS. 



Other Evaporation Masses. 



307. Joliet's Gum and Glycerin Method (Arch. Zool. exp. ei 

 gen., x, 1882, p. xliii; Journ. Roy. Mic. Soc. [N.S.], ii, 1882, 

 p. 890) . Pure gum arable dissolved in water to the consistency 

 of a thick syrup. (Solutions of gum sold under the name of 

 strong white liquid glue [" colle forte blanche liquide afroid" 

 may also be used ; they have the advantage of having a uni- 

 form consistency.*) Pour a little of the solution into a watch- 

 glass, so as not quite to fill it, add from 6 to 10 drops of pure 

 glycerin, stir until thoroughly mixed. 



Between the limits of 6 to 10 drops of glycerin the propor- 

 tions most suitable to the nature of the object and to the 

 season of the year must be found by experimental trials. In 

 the winter or in rainy weather less glycerin should be taken 

 than in the summer or dry weather. 



It is often well to soak the object in glycerin before putting 

 it into the mass. In this case less glycerin should be added 

 to the gum, in proportion to the amount of glycerin contained 

 in the object. 



The object is imbedded in the mass in the watch-glass, and 

 the whole left to dry for from one to four days. When it has 

 assumed a cartilaginous consistency, a block containing the 

 object is cut out, turned over, and allowed to dry again until 

 wanted for use. A stove, or the sun, may be employed for 

 drying, but it is best to dry slowly at the normal temperature. 

 The block may be preserved in good condition almost indefi- 

 nitely, the gum, when mixed with a sufficient quantity of 

 glycerin, never becoming hard or brittle. It is generally 

 better to wait till the blocks have assumed such a consistency 

 that they cannot be easily bent. It is after having waited 

 almost a week that the author always obtained the best sec- 

 tions. The gum is dissolved out from the sections by means 

 of a drop of water on the slide. The sections are then covered, 

 and a drop of glycerin being added, the preparation is com- 

 plete as soon as the water has evaporated. 



This mass has the advantage of being transparent. It 

 can be cut dry. Joliet employed it for Pyrosoma. A similar 

 mass was employed by Hertwig for Ctenophora (Jen. Zeitsch., 



* It is highly probable that these commercial preparations contain gelatin, 

 and perhaps some other gum besides gum arabic. 



