36 HISTOLOGICAL TECHNIC 



Busch's modification of the Marchi method gives sharp pictures 

 and has the advantage of allowing formaldehyd fixation and harden- 

 ing. Tissues thus treated are placed for from five to seven days in a 

 solution of one part osmic acid, three parts iodate of sodium, and 300 

 parts water. They are then embedded, cut, and mounted as usual. 



GoLGi Methods of Staining Nerve Tissue 



The Golgi methods in most common use at present are the fol- 

 lowing : 



(i) Golgi Silver Methods. — (a) Slow Method. — Blocks of tis- 

 sue are placed for several months in a 3-per-cent. aqueous solution of 

 potassium bichromate. Small pieces of the tissue are then trans- 

 ferred immediately to a 0.75-per-cent. aqueous solution of silver 

 nitrate. This is changed several times or until no more precipitate 

 is formed. In the last silver solution they remain for from one to 

 three days. The only method of determining whether the tissue has 

 been sufficiently long in the bichromate is to try at intervals small 

 bits of the tissue in the silver solution until a satisfactory result is 

 secured. Sections should usually be from 50 to 80 u thick and are 

 mounted in balsam without a cover-glass. 



(b) Rapid Method. — Small pieces of tissue, 2 to 4 mm. thick, are 

 placed in the following solution for from two to six days, the time 

 depending upon the age and character of the tissue, the temperature 

 at which fixation is carried on, and the elements which it is desired 

 to impregnate: 



Osmic acid, i-per-cent. aqueous solution, i part. 



Potassium bichromate, 3 . 5-per-cent. aqueous solution, 4 parts. 



As a rule, the longer the hardening the fewer are the elements stained, 

 but these few are clearer. The tissue is next transferred to silver 

 nitrate as in the slow method. Pieces of tissue should be tried each 

 day until a satisfactory result is obtained. The pieces may be kept 

 in silver nitrate some time, but not in alcohol, and are better cut with- 

 out embedding, the pieces being simply washed in 95-per-cent. 

 alcohol several hours, then gummed to the block with celloidin, cut in 

 95-per-cent. alcohol, and mounted as in the slow method. 



(c) Mixed Method. — Specimens are placed in the bichromate 

 solution for about four days, then from one to three days in the 

 osmium-bichromate mixture (see Rapid Method), after which they 

 are transferred to the silver solution (see Slow Method). 



