328 CENTRAL NERVOUS SYSTEM. 



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. 



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

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

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

 jected into the ventricles. 



The paraffin and collodion methods have already been sufficiently described 

 in Part I. 



Staining. 



673. Methods for General Stains. By a " general stain " is 

 here meant one by which it is intended to demonstrate as far 

 as possible all the histological elements of a preparation. 



Ammonia-carmine is one of the very best of these stains. 

 Beale's formula is a good one, especially where prolonged 

 staining is required. But in view of the greatest precision of 

 stain, the process of G-IERKE ( 137), or that of BETZ ( 136), 

 should be preferred. 



Picro-carmine is also an excellent reagent. It has much 

 the same action as ammonia-carmine, but gives a better de- 

 monstration of non-nervous elements. 



BEALE (Journ.Roy. Mic. Soc., 1886, p. 156) recommends that 

 the spinal cord of the ox be stained by immersion in toto for 

 twelve hours in picro-carmine. He states that he has found 

 no process that allows of following ganglion-cell processes 

 so far. 



Chromic objects stain very slowly in both these media. Sections may, 

 however, be stained with them in a few minutes if they be put into a watch- 

 glass with the stain, and the whole be kept on a wire net over a water-bath 

 heated to boiling point (OBEESTEINEE). 



UPSON (Neurolog. Centralb.,1888, p. 319 ; Zeit.f.wiss. Milt., v, 4, 1888, 

 p. 525) employs a stain made by adding to 5 c.c. of strong Grenadier's alum- 

 carmine 1 to 3 drops of phosphomolybdanic acid. In this, sections stain in 

 from two to ten minutes. 



He also employs a stain made by saturating alum-carmine with zinc sul- 

 phate. Sections stain in this in from half an hour to twelve hours. This is 

 said to give very ijood differentiations <>!' the elements of peripheral nerves. 



