188 MICROSCOPICAL TECHNIQUE. 



frozen. Or, as suggested by H. Plenge ( Virchoiv^s Archiv., Vol. 

 cxLiv., p. 409), the piece may be placed in a 4 per cent, formal- 

 dehyde solution for a quarter-of-an-hour, and then frozen in the 

 same solution. 



When the tissue has been prepared in some such manner, or 

 even when perfectly fresh, it is placed with some formol and gum 

 acacia fluid upon the specimen-holder of the microtome, and a 

 small stream of chloride, methyl chloride, or anestile (a mixture of 

 these two re-agents) is played from above directly upon the speci- 

 men. The tube containing the ethyl chloride is held about a foot 

 from the specimen, and moved from place to place until the spe- 

 cimen is firmly attached to its base of support, and the upper 

 portion is coated with a few crystals of ice. These crystals are 

 extremely small and delicate, and, therefore, do not injure the 

 tissue so markedly as in some other of the freezing methods. The 

 specimen is readily frozen in from thirty seconds to a minute. 

 Sections are then cut and placed in water or fifty per cent, alcohol, 

 and mounted in the usual way. Excellent stained preparations 

 may be prepared in fifteen minutes or less from the time that the 

 tissue is removed from the body. 



We hope to give a later and fuller report of this process at an 

 early date. H. W. Cattell. 



Formaldehyde in Pathological Work.— Orth (Berl. klin. Woch., 

 March 30th, 1896) draws attention to the value of this agent in 

 pathological work. Formol, or formalin, contains 40 per cent, 

 formaldehyde. It is generally known that formol is an excellent 

 hardening agent for most tissues, and especially for the brain, as 

 well as for red blood-cells, which it preserves and fixes. Both for 

 naked-eye and microscopic purposes the author has employed a 

 10 per cent, formal in Miiller's fluid. After two or three days this 

 solution becomes dark, and in four days a crystalline deposit 

 separates out. Thus the fluid requires changing in this time, but 

 mostly the hardening process is already completed. Small pieces 

 of tissue, measuring ^ to ^ cm. in thickness, are thoroughly 

 fixed and hardened in three hours in a warm chamber. Larger 

 pieces may remain overnight, and this time suffices for small pieces 

 at room temperature. The Miiller is washed out with water. The 



