THE METHODS OF IMBEDDING. 327 



671. Nervous Centres of Reptiles and Batrachia (MASON, Central 

 Nervous System of certain Reptiles, &c. ; WHITMAN'S Methods, p. 196), 

 Iodised alcohol, six to twelve hours ; 3 per cent, bichromate, with a piece 

 of camphor in the bottle, and to be changed once a fortnight until the 

 hardening is sufficient (six to ten weeks). 



Imbedding and Cutting. 



672. The Methods of Imbedding. The paraffin infiltration 

 method can only be used for the smaller objects of this class. 

 Human spinal cord (which is quite at the upper limit as re- 

 gards size) can be properly penetrated with paraffin by taking 

 the precaution of first cutting it up into slices of not more 

 than 1 millimetre in thickness. The largest objects of this 

 class, such as entire hemispheres of man, cannot be properly 

 penetrated by any known imbedding mass ; and the anatomist 

 must be content with simple 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 con- 

 venient, and the most advantageous as regards the ulterior 

 treatment of sections. 



BEVAN 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, 

 308. 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 the entire human brain, DEECKE (1. c.) proceeds as follows: 

 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 

 tin' 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 



