58 Neurological Technique 



period to prevent a too rapid reduction of the silver on the sur- 

 face of the pieces of tissue. 



Change the silver solution after 8-12 hours. The tissue may 

 remain in the silver solution 5 or 6 days without injury. 



4. To imbed in celloidin. — Sections of the tissue may be made 

 "free-hand" with a razor and examined under the microscope 

 to see whether the elements are stained. For permanent use 

 microtome sections are best. The tissue should be carried 

 through the imbedding and sectioning process and mounted as 

 quickly as possible, since the metallic deposit, which is the nature 

 of the impregnation, tends to break up in fluids other than the 

 silver solution. 



As a matter of caution, imbed only a few of the pieces at a 

 time, leaving the remainder in the silver nitrate solution, lest fur- 

 ther treatment should prove necessary. 



{a) To dehydrate, transfer the dark-brown pieces from the 

 silver solution directly to about 20 times their volume of 95 per 

 cent, alcohol for 20 minutes. Renew the alcohol after the first five 

 minutes and occasionally agitate. 



{b^ Replace the 95 per cent, with the same amount of abso- 

 lute alcohol for 30 minutes. 



Renew the absolute after iq minutes, agitating as before. 



(c) Replace the absolute alcohol with 20-30 volumes of 

 ether-alcohol (D) for 20 minutes. 



(d) Transfer to enough thin celloidin (E, i) to well cover the 

 pieces for 25 minutes. 



{e) Replace thin celloidin with thick celloidin (E, 2) for 10 

 minutes. 



(/) Prepare wooden or cork blocks of suitable size and such 

 as will fit the object-carrier of the microtome. Dip the end of 

 a block into ether-alcohol and then place upon it, in position for 

 sectioning, one of the pieces of tissue well covered in thick cel- 

 loidin. Keeping the piece in position, harden the celloidin by 

 placing the whole in a small amount of chloroform for about 10 

 minutes. 



[g) Transfer the block from chloroform to a stender dish of 

 the clearing fluid ,( F) for 15-30 minutes. 



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