THE METHODS OF IMBEDDING. 393 



hemispheres of man, cannot be properly penetrated by any 

 known imbedding mass ; and the anatomist must be content 

 "with simple superficial imbedding a proceeding which is 

 here of the greatest service. For intermediate objects those 

 whose size varies between that of a small nut and a walnut 

 it appears to me that no hesitation as to the proper course is 

 possible; such objects should be treated by the collodion 

 method, which is at once the safest, the most convenient, and 

 the most advantageous, as regards the ulterior treatment of 

 sections. 



BE VAN LEWIS recommends the ether freezing method for fresh brain. 

 For hardened brain he recommends some of the old-fashioned wax-and-oil 

 and other fatty mixtures, a doctrine at which I am surprised. 



HAMILTON recommends freezing in the gum and syrup mass given above, 

 316. He also recommends a method of penetrating with collodion, which 

 is hardened in the usual way, the hardened mass being cut with an ice-and- 

 salt freezing microtome (see Journ. of Anat. and Physiol., 1887, p. 444 ; or 

 Journ. Roy. Mic. Soc., 1888, p. 1051). 



For sections of entire human brain, DEECZE (1. c., 738) proceeds as fol- 

 lows : The brain to be cut is placed upon the piston of the microtome (a 

 Ranvier model) and held in situ by several pieces of soft cork. It is then 

 imbedded in a cast of paraffin, olive oil, and tallow, which, after it has 

 become hard, is held in position by a number of small curved rods attached 

 to, and projecting upwards from, the piston to the height of about an inch. 

 Before cutting, and as it proceeds, the cast is carefully removed from around 

 the specimen to the depth of about half an inch (which is easily done by the 

 use of a good-sized carpenter's chisel), so that the knife never comes in 

 contact with the cast. 



Cutting is done under alcohol, the entire microtome being immersed in a 

 copper basin. The sections are floated, with the aid of a fine camel-hair 

 brush, on to sheets of glazed writing-paper. They are removed thereon 

 successively into staining, washing, and clearing fluids. After clearing, 

 they are brought on the paper on to a slide, and the paper is gently pulled 

 away from them ; they are then mounted in chloroform- or benzol-balsam. 



It should be noted that the membranes should not be removed from the 

 brain ; they present no obstacle to cutting if this is done with a slight 

 sawing movement, or with a series of short cuts, instead of one sweep of 

 the knife. By this plan the sections are much more perfect and uniform in 

 thickness, and the loss in a series of from four to five hundred to the inch 

 through the entire cerebrum of man may not amount to more than 2 or 

 3 per cent. 



OSBOEN (Proc. Acad. Nat. Sci. Philadelphia, 1883, p. 178, and 1884, 

 p. 262 ; WHITMAN'S Methods, p. 195) found advantage in employing Euge's 

 egg-mass (for the brain of Urodela). He recommends that the mass be 

 injected into the ventricles. 



The paraffin and collodion methods have already been sufficiently described 

 in Part I. 



