APPENDIX. 365 



used alone usually causes more or less shrinking and 

 distortion, of the outer parts of the tissue ; in such 

 case the inner part only should be taken in pre- 

 paring sections. 



Imbedding. 



Take a smaU piece of tissue only to imbed ; of course 

 this cannot be done in many cases, where it is 

 desired to make out the general relation of the parts 

 of an organ ; it is moreover of comparatively little 

 importance when the sections are to be cut with 

 a microtome. 



Before imbedding (cp. p. 68) press the piece of tissue 

 very gently between blotting-paper, to remove as 

 much as possible of the fluid in which it has been 

 placed. The fluid, if not removed, cools the imbed- 

 ding mixture immediately round the tissue, and not 

 mixing with it prevents the due adhesion between 

 the mixture and the tissue : with spirit specimens 

 "the excess of fluid should not be removed tiU the 

 imbedding substance, etc., is ready, since the spirit 

 rapidly evaporates, and the tissue may become dry. 



The imbedding substance should be heated as little as 

 possible above its melting point. To keep it at a 

 constant temperature, a water-bath heated by a 

 small gas jet with a regulator may with advantage 

 be used. 



When the tissue is moved about by means of a heated 

 needle, to place it in position in the embedding 

 substance or to remove air-bubbles, bring down the 

 temperature of the needle to that of the substance 

 by moving the needle about in it before touching 

 the tissue. 



