CHAPTER III 

 KILLING AND FIXING 



CAUTIONS. 1. Use only fresh tissues and work rapidly so 

 that the tissue elements will not have time to undergo postmortem 

 changes. 



2. Remove organs carefully, and avoid crushing or pressing 

 the parts to be prepared. 



3. Tissues should never be allowed to dry from the time they 

 leave the animal until they are finally mounted for microscopical 

 examination except at one point in the paraffin method. 



4. Use only small pieces (2 to 6 mm. cube) of tissue whenever 

 possible, or penetration of the reagent will be insufficient. 

 Embryos and small objects up to 4 cm. in size may be placed 

 entire in certain oj the fixing fluids. 



5. For fixing and hardening, the bulk of the fluid should be 

 from 10 to 50 times that of the object. Too many pieces should 

 not be placed in the same vial. 



6. Use only clean reagents. It is well to let the object rest on 

 a bit of cotton in the bottom of the vial or have it suspended from 

 the vial mouth so that the reagent may penetrate equally from all 

 sides. Penetration is aided by heat. 



7. When necessary to wash fresh tissue, it is usually best to 

 use normal saline, and not water. Let it flow gently over the 

 surface of the object or slowly twirl the latter in the fluid. Do 

 not scrape off foreign matter. 



8. In many cases the killing and fixing reagent does not 

 harden the tissue sufficiently and the hardening process must be 

 completed in alcohol. 



9. Keep the reagents and preparations from direct sunlight. 



10. Carefully label each vessel containing tissue. State the 

 contents, the fluid used, and the date. Label on the side. 



11. Keep a careful record on cards of the reagents used, and 

 the time ivhen changed, for each separate piece of tissue. 



27 



