Protocerehrum of Micropteryx. 145 



will completely ruin the preparations.) The slides are now 

 placed in 1-2 % AgNOg and exposed to bright sunlight or 

 an electric lamp for about ten minutes. After this they 

 are Avashed for two minutes in distilled water and placed in 

 1 % gold chloride for two minutes in a bright light. They 

 are then again washed and placed in an aqueous solution of 

 pyrogallic acid until the reduction is complete, deposits of 

 metal being left in the fibres. The sections are now brought 

 up through the usual grades of alcohol, stained for a very 

 few seconds in orange G, and mounted. These prepara- 

 tions do not degenerate under the cover-slip in the same 

 manner as Golgi preparations. 



This impregnation is only a modification of one intro- 

 duced by Ramon y Cajal; a similar method has been 

 employed by Jonescu. 



If it is successful it gives sweeping black lines of axons 

 running through the brain in the most diagrammatic 

 manner. It is unfortunately almost inapplicable to so 

 small an insect as Micropteryx, owing to the fact that the 

 aqueous silver solution hardly penetrates the insect's 

 minute neck even after decapitation. I am quite confident 

 that this method will be found most useful in the study of 

 the brains of insects which are large enough to admit of 

 the brain being laid partly bare to the fixing fluid. 



II. Section Cutting. 



All material should be stored in 90% alcohol, rather than 

 in a lower percentage. Excellent material may be com- 

 pletely ruined if the spirit in which it is kept has ever been 

 in contact with cork, the tannin of which interferes with 

 the action of most stains : glass-stoppered vessels must 

 accordingly be used. 



Section Cutting. — It is well known that the cutting of 

 sections through heavily chitinous insects presents great 

 difficulties. Much may be done to overcome this, but be- 

 fore discussing methods of softening chitin I should like 

 to state my firm con\dction that the one factor of prime 

 importance is the microtome knife. In the absence of a 

 really sharp knife no softening reagents and no care exer- 

 cised during the embedding are of the slightest value. The 

 best softening reagent, so far as my limited knowledge goes, 

 is spirit soap (German Pharmacopoeia), the use of which was 

 first advocated by Kurt Bedau. The insects are placed in 



TRANS. ENT. SOC. LOND. 1917. — PART I. (NOV.) L 



