322 Transactions of the Society. 



emphasized by pointing out that the former involves an opaque 

 deposit of a metallic compound around tissue elements, whereas in 

 staining the dye is absorhed by these, so that they retain more or less 

 their transparency. But, as pointed out by Lee {8), successful 

 impregnations frequently show all the gradations between the two 

 extremes. Thus in preparations by Cajal's method of the Golgi 

 apparatus the latter may be impregnated black, while the ground 

 cytoplasm is stained yellow. 



2. Technique of Cajal's Method for the Golgi 



Apparatus. 



This process was first introduced in its present form by Cajal 

 in 1912 (.^). The following notes have been extracted from that 

 author's most recent account of his technique accessible to me {!) : — 



1. Fixation. — Pieces of tissue are thrown into — 



Formol (40p.c.) .... 15 c.cm. 



Aq. dest. 85 ,, 



Uranium nitrate .... l.grm. 



Material remains in this for ten to fourteen hours. For the 

 fixation of large masses of tissue Cajal advises a preliminary injec- 

 tion with the fixative before immersion. 



For the central nervous system, or for tissues difficult to 

 impregnate, fix in — 



Absolute ethyl or methyl alcohol . 30 c.cm. 



Aq. dest. 80 „ 



Formol (40 p.c.) . . . 15-20 ,. 

 Uranium nitrate .... 1 grm. 



2. Wash rapidly in distilled water — a few seconds will suffice. 



3. Impregnate with a 1*5 p.c. solution of silver nitrate for 

 thii'ty-six to forty-eight hours at room temperature. 



4. Wash rapidly in distilled water. 



5. Eeduce for from eight to twenty-four hours in the following 

 fluid :— 



Hydroquinone .... 1-2 grm. 



Formol (40 p.c.) .... 15 c.cm. 



Aq. dest - . . 100 „ 



Sodium sulphite .... 0"5grm. 



The addition of the NaaSOg causes the solution to go pale yellow. 



6. Wash in water, dehydrate in ascending grades of alcohol, and 

 embed in either paraffin or celloidin ; or sections may be cut with 

 the freezing microtome. But the paraffin method is the most 

 satisfactory for general purposes. 



7. Sections on the slide may be toned if necessary, the process 



