72 Animal Micrology 



4. Transfer a few of 'the brown pieces of tissue to 95 per cent, 

 alcohol for half an hour, renewing it once or twice during this 

 time. Leave the rest of the tissue in the silver-nitrate solution 

 for future use in case the first attempt proves unsuccessful. 



5. Remove the pieces from 95 per cent, to absolute alcohol for 

 20 minutes, changing the latter once. Then transfer them to 

 ether-alcohol for 20 minutes. 



6. Imbed in celloidiri without waiting for infiltration to occur 

 (thin celloidin 30 minutes, thick celloidin 10 minutes). Mount 

 directly on a block and harden in chloroform for 20 minutes. 



7. From chloroform transfer directly to the clearing fluid 

 (e. g., cedar oil), and as soon as clear (30 to 60 minutes) cut sec- 

 tions 50 to 100 microns thick, only keep the knife flooded with 

 the clearing fluid instead of alcohol. Cut sections of cortex so 

 that they will be perpendicular to the surface of the brain. 



8. When the sections are thoroughly cleared, transfer them to 

 a slide flooded with the clearing fluid, select such as prove desir- 

 able upon microscopic inspection, and discard the remainder. 



9. Replace the oil with xylol, then remove the xylol by press- 

 ing upon the sections with blotting paper. Add enough thick 

 Canada balsam to cover the sections. 



Caution. Do not put on a cover-glass; moisture must evapo- 

 rate from the section. If this is prevented the metal deposits 

 break up and the sections become worthless. 



10. Keep the preparations level and put them away in a dry 

 place free from dust. If the balsam runs off the sections more 

 balsam must be added at once. Do not attempt to examine under 

 a high power until the balsam is thoroughly hardened. 



MEMORANDA 



1. A Fuller Account of the Golgi Methods will be found in Hardesty's 

 Neurological Technique (pp. 55-61), or in Lee's Microtomisfs Vade- 

 Mecum (pp. 411-27). 



2. An Osmium-Bichromate Mixture is frequently used instead of for- 

 malin for fixing fresh tissues. To 85 parts of a 3.5 per cent, solution 

 of potassium bichromate add 15 parts of a 1 per cent, solution of osmic 

 acid. Small pieces (4 to 6 mm. thick) of fresh tissue are placed iu 40 

 times their volume of this mixture and kept in the dark for from 12 to 24 



